Add support for pipes in templates #53

The goal is to be able to modify values of variables used in templates. It enables future functionality such as escaping, inlining etc. It adds support applying predefined pipes to variables. Pipes can be applied to variable substitution in with and parameter substitution expressions. They work in similar way to piping in Unix where each pipe applied to the compiled result of pipe before. It adds support for using pipes in `with` and parameter substitution expressions. It also refactors how their regex is build to reuse more of the logic by abstracting regex building into a new class. Finally, it separates and extends documentation for templating.
2021-09-08 18:58:30 +01:00
parent 862914b06e
commit 4d7ff7edc5
30 changed files with 1112 additions and 207 deletions
--- a/README.md
+++ b/README.md
@@ -30,7 +30,8 @@
 - Have full visibility into what the tweaks do as you enable them
 - Ability to revert (undo) applied scripts
 - Everything is transparent: both application and its infrastructure are open-source and automated
- Easily extendable
+- Easily extendable with [own powerful templating language](./docs/templating.md)
+- Each script is independently executable without cross-dependencies

 ## Extend scripts

--- a/docs/collection-files.md
+++ b/docs/collection-files.md
@@ -80,7 +80,7 @@
 ### `FunctionCall`

 - Describes a single call to a function by optionally providing values to its parameters.
- 👀 See [parameter substitution](#parameter-substitution) for an example usage
+- 👀 See [parameter substitution](./templating.md#parameter-substitution) for an example usage

 #### `FunctionCall` syntax

@@ -100,73 +100,10 @@

 ### `Function`

- Functions allow re-usable code throughout the defined scripts.
- Functions are templates compiled by privacy.sexy and uses special [expressions](#expressions).
+- Functions allow re-usable code throughout the defined scripts
+- Functions are templates compiled by privacy.sexy and uses special expression expressions
 - Functions can call other functions by defining `call` property instead of `code`
- 👀 See [parameter substitution](#parameter-substitution) for an example usage
-
-#### Expressions
-
- Expressions are defined inside mustaches (double brackets, `{{` and `}}`)
- Expression syntax is inspired by [Go Templates](https://pkg.go.dev/text/template)
-
-##### Parameter substitution
-
-A simple function example
-
-```yaml
-  function: EchoArgument
-  parameters:
-    - name: 'argument'
-  code: Hello {{ $argument }} !
-```
-
-It would print "Hello world" if it's called in a [script](#script) as following:
-
-```yaml
-  script: Echo script
-  call:
-    function: EchoArgument
-    parameters:
-      argument: World
-```
-
-A function can call other functions such as:
-
-```yaml
-  - 
-    function: CallerFunction
-    parameters:
-      - name: 'value'
-    call:
-      function: EchoArgument
-      parameters:
-        argument: {{ $value }}
-  -
-    function: EchoArgument
-    parameters:
-      - name: 'argument'
-    code: Hello {{ $argument }} !
-```
-
-##### with
-
- Skips the block if the variable is absent or empty.
- Binds its context (`.`) value of provided argument for the parameter only if its value is provided.
- A block is defined as `{{ with $parameterName }} Parameter value is {{ . }} here {{ end }}`
- The parameters used for `with` condition should be declared as optional, otherwise `with` block becomes redundant.
- Example:
-
-  ```yaml
-    function: FunctionThatOutputsConditionally
-    parameters:
-      - name: 'argument'
-        optional: true
-    code: |- 
-      {{ with $argument }}
-        $argument's value is: {{ . }}
-      {{ end }}
-  ```
+- 👀 Read more on [Templating](./templating.md) for function expressions and [example usages](./templating.md#parameter-substitution)

 #### `Function` syntax

@@ -177,7 +114,7 @@ A function can call other functions such as:
  - ❗ Function names must be unique
 - `parameters`: `[` ***[`FunctionParameter`](#FunctionParameter)*** `, ... ]`
  - List of parameters that function code refers to.
-  - ❗ Must be defined to be able use in [`FunctionCall`](#functioncall) or [expressions](#expressions)
+  - ❗ Must be defined to be able use in [`FunctionCall`](#functioncall) or [expressions](./templating.md#expressions)
 `code`: *`string`* (**required** if `call` is undefined)
  - Batch file commands that will be executed
  - 💡 If defined, best practice to also define `revertCode`
@@ -188,7 +125,7 @@ A function can call other functions such as:
    - then `revertCode` should be doing `setx POWERSHELL_TELEMETRY_OPTOUT 0`
 - `call`: ***[`FunctionCall`](#FunctionCall)*** | `[` ***[`FunctionCall`](#FunctionCall)*** `, ... ]` (may be **required**)
  - A shared function or sequence of functions to call (called in order)
-  - The parameter values that are sent can use [expressions](#expressions)
+  - The parameter values that are sent can use [expressions](./templating.md#expressions)
  - ❗ If not defined `code` must be defined

 ### `FunctionParameter`
@@ -200,7 +137,7 @@ A function can call other functions such as:

 - `name`: *`string`* (**required**)
  - Name of the parameters that the function has.
-  - Parameter names must be defined to be used in [expressions](#expressions).
+  - Parameter names must be defined to be used in [expressions](./templating.md#expressions).
  - ❗ Parameter names must be unique and include alphanumeric characters only.
 - `optional`: *`boolean`* (default: `false`)
  - Specifies whether the caller [Script](#script) must provide any value for the parameter.
@@ -208,7 +145,7 @@ A function can call other functions such as:
    - Otherwise it throws.
  - 💡 Set it to `true` if a parameter is used conditionally;
    - Or else set it to `false` for verbosity or do not define it as default value is `false` anyway.
-  - 💡 Can be used in conjunction with [`with` expression](#with).
+  - 💡 Can be used in conjunction with [`with` expression](./templating.md#with).

 ### `ScriptingDefinition`

@@ -220,7 +157,7 @@ A function can call other functions such as:
  - 📖 See [ScriptingLanguage.ts](./../src/domain/ScriptingLanguage.ts) enumeration for allowed values.
 - `startCode:` *`string`* (**required**)
  - Code that'll be inserted on top of user created script.
-  - Global variables such as `$homepage`, `$version`, `$date` can be used using [parameter substitution](#parameter-substitution) code syntax such as `Welcome to {{ $homepage }}!`
+  - Global variables such as `$homepage`, `$version`, `$date` can be used using [parameter substitution](./templating.md#parameter-substitution) code syntax such as `Welcome to {{ $homepage }}!`
 - `endCode:` *`string`* (**required**)
  - Code that'll be inserted at the end of user created script.
-  - Global variables such as `$homepage`, `$version`, `$date` can be used using [parameter substitution](#parameter-substitution) code syntax such as `Welcome to {{ $homepage }}!`
+  - Global variables such as `$homepage`, `$version`, `$date` can be used using [parameter substitution](./templating.md#parameter-substitution) code syntax such as `Welcome to {{ $homepage }}!`
--- a/docs/templating.md
+++ b/docs/templating.md
@@ -0,0 +1,81 @@
+# Templating
+
+## Benefits of templating
+
+- Generating scripts by sharing code to increase best-practice usage and maintainability.
+- Creating self-contained scripts without depending on each other that can be easily shared.
+- Use of pipes for writing cleaner code and letting pipes do dirty work.
+
+## Expressions
+
+- Expressions in the language are defined inside mustaches (double brackets, `{{` and `}}`).
+- Expression syntax is inspired mainly by [Go Templates](https://pkg.go.dev/text/template).
+
+## Syntax
+
+### Parameter substitution
+
+A simple function example:
+
+```yaml
+  function: EchoArgument
+  parameters:
+    - name: 'argument'
+  code: Hello {{ $argument }} !
+```
+
+It would print "Hello world" if it's called in a [script](./collection-files.md#script) as following:
+
+```yaml
+  script: Echo script
+  call:
+    function: EchoArgument
+    parameters:
+      argument: World
+```
+
+A function can call other functions such as:
+
+```yaml
+  - 
+    function: CallerFunction
+    parameters:
+      - name: 'value'
+    call:
+      function: EchoArgument
+      parameters:
+        argument: {{ $value }}
+  -
+    function: EchoArgument
+    parameters:
+      - name: 'argument'
+    code: Hello {{ $argument }} !
+```
+
+### with
+
+- Skips the block if the variable is absent or empty.
+- Binds its context (`.`) value of provided argument for the parameter if provided one.
+- A block is defined as `{{ with $parameterName }} Parameter value is {{ . }} here {{ end }}`.
+- The parameters used for `with` condition should be declared as optional, otherwise `with` block becomes redundant.
+- Example:
+
+  ```yaml
+    function: FunctionThatOutputsConditionally
+    parameters:
+      - name: 'argument'
+        optional: true
+    code: |- 
+      {{ with $argument }}
+        Value is: {{ . }}
+      {{ end }}
+  ```
+
+### Pipes
+
+- Pipes are set of functions available for handling text in privacy.sexy.
+- Allows stacking actions one after another also known as "chaining".
+- Just like [Unix pipelines](https://en.wikipedia.org/wiki/Pipeline_(Unix)), the concept is simple: each pipeline's output becomes the input of the following pipe.
+- Pipes are provided and defined by the compiler and consumed by collection files.
+- Pipes can be combined with [parameter substitution](#parameter-substitution) and [with](#with).
+- ❗ Pipe names must be camelCase without any space or special characters.
--- a/src/application/Parser/Script/Compiler/Expressions/Expression/Expression.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Expression/Expression.ts
@@ -4,8 +4,10 @@ import { IReadOnlyFunctionCallArgumentCollection } from '../../FunctionCall/Argu
 import { IReadOnlyFunctionParameterCollection } from '../../Function/Parameter/IFunctionParameterCollection';
 import { FunctionParameterCollection } from '@/application/Parser/Script/Compiler/Function/Parameter/FunctionParameterCollection';
 import { FunctionCallArgumentCollection } from '../../FunctionCall/Argument/FunctionCallArgumentCollection';
+import { IExpressionEvaluationContext } from './ExpressionEvaluationContext';
+import { ExpressionEvaluationContext } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext';

-export type ExpressionEvaluator = (args: IReadOnlyFunctionCallArgumentCollection) => string;
+export type ExpressionEvaluator = (context: IExpressionEvaluationContext) => string;
 export class Expression implements IExpression {
    constructor(
        public readonly position: ExpressionPosition,
@@ -18,13 +20,14 @@ export class Expression implements IExpression {
            throw new Error('undefined evaluator');
        }
    }
-    public evaluate(args: IReadOnlyFunctionCallArgumentCollection): string {
-        if (!args) {
-            throw new Error('undefined args, send empty collection instead');
+    public evaluate(context: IExpressionEvaluationContext): string {
+        if (!context) {
+            throw new Error('undefined context');
        }
-        validateThatAllRequiredParametersAreSatisfied(this.parameters, args);
-        args = filterUnusedArguments(this.parameters, args);
-        return this.evaluator(args);
+        validateThatAllRequiredParametersAreSatisfied(this.parameters, context.args);
+        const args = filterUnusedArguments(this.parameters, context.args);
+        context = new ExpressionEvaluationContext(args, context.pipelineCompiler);
+        return this.evaluator(context);
    }
 }

--- a/src/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext.ts
@@ -0,0 +1,18 @@
+import { IReadOnlyFunctionCallArgumentCollection } from '../../FunctionCall/Argument/IFunctionCallArgumentCollection';
+import { IPipelineCompiler } from '../Pipes/IPipelineCompiler';
+import { PipelineCompiler } from '../Pipes/PipelineCompiler';
+
+export interface IExpressionEvaluationContext {
+    readonly args: IReadOnlyFunctionCallArgumentCollection;
+    readonly pipelineCompiler: IPipelineCompiler;
+}
+
+export class ExpressionEvaluationContext implements IExpressionEvaluationContext {
+    constructor(
+        public readonly args: IReadOnlyFunctionCallArgumentCollection,
+        public readonly pipelineCompiler: IPipelineCompiler = new PipelineCompiler()) {
+        if (!args) {
+            throw new Error('undefined args, send empty collection instead');
+        }
+    }
+}
--- a/src/application/Parser/Script/Compiler/Expressions/Expression/IExpression.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Expression/IExpression.ts
@@ -1,9 +1,9 @@
 import { ExpressionPosition } from './ExpressionPosition';
-import { IReadOnlyFunctionCallArgumentCollection } from '../../FunctionCall/Argument/IFunctionCallArgumentCollection';
 import { IReadOnlyFunctionParameterCollection } from '../../Function/Parameter/IFunctionParameterCollection';
+import { IExpressionEvaluationContext } from './ExpressionEvaluationContext';

 export interface IExpression {
    readonly position: ExpressionPosition;
    readonly parameters: IReadOnlyFunctionParameterCollection;
-    evaluate(args: IReadOnlyFunctionCallArgumentCollection): string;
+    evaluate(context: IExpressionEvaluationContext): string;
 }
--- a/src/application/Parser/Script/Compiler/Expressions/ExpressionsCompiler.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/ExpressionsCompiler.ts
@@ -3,6 +3,8 @@ import { IExpression } from './Expression/IExpression';
 import { IExpressionParser } from './Parser/IExpressionParser';
 import { CompositeExpressionParser } from './Parser/CompositeExpressionParser';
 import { IReadOnlyFunctionCallArgumentCollection } from '../FunctionCall/Argument/IFunctionCallArgumentCollection';
+import { ExpressionEvaluationContext } from './Expression/ExpressionEvaluationContext';
+import { IExpressionEvaluationContext } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext';

 export class ExpressionsCompiler implements IExpressionsCompiler {
    public constructor(
@@ -15,7 +17,8 @@ export class ExpressionsCompiler implements IExpressionsCompiler {
        }
        const expressions = this.extractor.findExpressions(code);
        ensureParamsUsedInCodeHasArgsProvided(expressions, args);
-        const compiledCode = compileExpressions(expressions, code, args);
+        const context = new ExpressionEvaluationContext(args);
+        const compiledCode = compileExpressions(expressions, code, context);
        return compiledCode;
    }
 }
@@ -23,7 +26,7 @@ export class ExpressionsCompiler implements IExpressionsCompiler {
 function compileExpressions(
    expressions: readonly IExpression[],
    code: string,
-    args: IReadOnlyFunctionCallArgumentCollection): string {
+    context: IExpressionEvaluationContext) {
    let compiledCode = '';
    const sortedExpressions = expressions
        .slice() // copy the array to not mutate the parameter
@@ -33,7 +36,7 @@ function compileExpressions(
        const nextExpression = sortedExpressions.pop();
        if (nextExpression) {
            compiledCode += code.substring(index, nextExpression.position.start);
-            const expressionCode = nextExpression.evaluate(args);
+            const expressionCode = nextExpression.evaluate(context);
            compiledCode += expressionCode;
            index = nextExpression.position.end;
        } else {
--- a/src/application/Parser/Script/Compiler/Expressions/Parser/Regex/ExpressionRegexBuilder.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Parser/Regex/ExpressionRegexBuilder.ts
@@ -0,0 +1,59 @@
+export class ExpressionRegexBuilder {
+    private readonly parts = new Array<string>();
+
+    public expectCharacters(characters: string) {
+        return this.addRawRegex(
+            characters
+                .replaceAll('$', '\\$')
+                .replaceAll('.', '\\.'),
+        );
+    }
+
+    public expectOneOrMoreWhitespaces() {
+        return this
+            .addRawRegex('\\s+');
+    }
+
+    public matchPipeline() {
+        return this
+            .expectZeroOrMoreWhitespaces()
+            .addRawRegex('(\\|\\s*.+?)?');
+    }
+
+    public matchUntilFirstWhitespace() {
+        return this
+            .addRawRegex('([^|\\s]+)');
+    }
+
+    public matchAnythingExceptSurroundingWhitespaces() {
+        return this
+            .expectZeroOrMoreWhitespaces()
+            .addRawRegex('(.+?)')
+            .expectZeroOrMoreWhitespaces();
+    }
+
+    public expectExpressionStart() {
+        return this
+            .expectCharacters('{{')
+            .expectZeroOrMoreWhitespaces();
+    }
+
+    public expectExpressionEnd() {
+        return this
+            .expectZeroOrMoreWhitespaces()
+            .expectCharacters('}}');
+    }
+
+    public buildRegExp(): RegExp {
+        return new RegExp(this.parts.join(''), 'g');
+    }
+
+    private expectZeroOrMoreWhitespaces() {
+        return this
+            .addRawRegex('\\s*');
+    }
+    private addRawRegex(regex: string) {
+        this.parts.push(regex);
+        return this;
+    }
+}
--- a/src/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser.ts
@@ -1,9 +1,9 @@
-import { IExpressionParser } from './IExpressionParser';
-import { ExpressionPosition } from '../Expression/ExpressionPosition';
-import { IExpression } from '../Expression/IExpression';
-import { Expression, ExpressionEvaluator } from '../Expression/Expression';
-import { IFunctionParameter } from '../../Function/Parameter/IFunctionParameter';
-import { FunctionParameterCollection } from '../../Function/Parameter/FunctionParameterCollection';
+import { IExpressionParser } from '../IExpressionParser';
+import { ExpressionPosition } from '../../Expression/ExpressionPosition';
+import { IExpression } from '../../Expression/IExpression';
+import { Expression, ExpressionEvaluator } from '../../Expression/Expression';
+import { IFunctionParameter } from '../../../Function/Parameter/IFunctionParameter';
+import { FunctionParameterCollection } from '../../../Function/Parameter/FunctionParameterCollection';

 export abstract class RegexParser implements IExpressionParser {
    protected abstract readonly regex: RegExp;
--- a/src/application/Parser/Script/Compiler/Expressions/Pipes/IPipe.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Pipes/IPipe.ts
@@ -0,0 +1,4 @@
+export interface IPipe {
+    readonly name: string;
+    apply(input: string): string;
+}
--- a/src/application/Parser/Script/Compiler/Expressions/Pipes/IPipelineCompiler.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Pipes/IPipelineCompiler.ts
@@ -0,0 +1,3 @@
+export interface IPipelineCompiler {
+    compile(value: string, pipeline: string): string;
+}
--- a/src/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory.ts
@@ -0,0 +1,42 @@
+import { IPipe } from './IPipe';
+
+const RegisteredPipes = [ ];
+
+export interface IPipeFactory {
+    get(pipeName: string): IPipe;
+}
+
+export class PipeFactory implements IPipeFactory {
+    private readonly pipes = new Map<string, IPipe>();
+    constructor(pipes: readonly IPipe[] = RegisteredPipes) {
+        if (pipes.some((pipe) => !pipe)) {
+            throw new Error('undefined pipe in list');
+        }
+        for (const pipe of pipes) {
+            this.registerPipe(pipe);
+        }
+    }
+    public get(pipeName: string): IPipe {
+        validatePipeName(pipeName);
+        if (!this.pipes.has(pipeName)) {
+            throw new Error(`Unknown pipe: "${pipeName}"`);
+        }
+        return this.pipes.get(pipeName);
+    }
+    private registerPipe(pipe: IPipe): void {
+        validatePipeName(pipe.name);
+        if (this.pipes.has(pipe.name)) {
+            throw new Error(`Pipe name must be unique: "${pipe.name}"`);
+        }
+        this.pipes.set(pipe.name, pipe);
+    }
+}
+
+function validatePipeName(name: string) {
+    if (!name) {
+        throw new Error('empty pipe name');
+    }
+    if (!/^[a-z][A-Za-z]*$/.test(name)) {
+        throw new Error(`Pipe name should be camelCase: "${name}"`);
+    }
+}
--- a/src/application/Parser/Script/Compiler/Expressions/Pipes/PipelineCompiler.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/Pipes/PipelineCompiler.ts
@@ -0,0 +1,31 @@
+import { IPipeFactory, PipeFactory } from './PipeFactory';
+import { IPipelineCompiler } from './IPipelineCompiler';
+
+export class PipelineCompiler implements IPipelineCompiler {
+    constructor(private readonly factory: IPipeFactory = new PipeFactory()) { }
+    public compile(value: string, pipeline: string): string {
+        ensureValidArguments(value, pipeline);
+        const pipeNames = extractPipeNames(pipeline);
+        const pipes = pipeNames.map((pipeName) => this.factory.get(pipeName));
+        for (const pipe of pipes) {
+            value = pipe.apply(value);
+        }
+        return value;
+    }
+}
+
+function extractPipeNames(pipeline: string): string[] {
+    return pipeline
+        .trim()
+        .split('|')
+        .slice(1)
+        .map((p) => p.trim());
+}
+
+function ensureValidArguments(value: string, pipeline: string) {
+    if (!value) { throw new Error('undefined value'); }
+    if (!pipeline) { throw new Error('undefined pipeline'); }
+    if (!pipeline.trimStart().startsWith('|')) {
+        throw new Error('pipeline does not start with pipe');
+    }
+}
--- a/src/application/Parser/Script/Compiler/Expressions/SyntaxParsers/ParameterSubstitutionParser.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/SyntaxParsers/ParameterSubstitutionParser.ts
@@ -1,13 +1,28 @@
-import { RegexParser, IPrimitiveExpression } from '../Parser/RegexParser';
+import { RegexParser, IPrimitiveExpression } from '../Parser/Regex/RegexParser';
 import { FunctionParameter } from '@/application/Parser/Script/Compiler/Function/Parameter/FunctionParameter';
+import { ExpressionRegexBuilder } from '../Parser/Regex/ExpressionRegexBuilder';

 export class ParameterSubstitutionParser extends RegexParser {
-    protected readonly regex = /{{\s*\$([^}| ]+)\s*}}/g;
+    protected readonly regex = new ExpressionRegexBuilder()
+        .expectExpressionStart()
+        .expectCharacters('$')
+        .matchUntilFirstWhitespace()    // First match: Parameter name
+        .matchPipeline()                // Second match: Pipeline
+        .expectExpressionEnd()
+        .buildRegExp();
+
    protected buildExpression(match: RegExpMatchArray): IPrimitiveExpression {
        const parameterName = match[1];
+        const pipeline = match[2];
        return {
            parameters: [ new FunctionParameter(parameterName, false) ],
-            evaluator: (args) => args.getArgument(parameterName).argumentValue,
+            evaluator: (context) => {
+                const argumentValue = context.args.getArgument(parameterName).argumentValue;
+                if (!pipeline) {
+                    return argumentValue;
+                }
+                return context.pipelineCompiler.compile(argumentValue, pipeline);
+            },
        };
    }
 }
--- a/src/application/Parser/Script/Compiler/Expressions/SyntaxParsers/WithParser.ts
+++ b/src/application/Parser/Script/Compiler/Expressions/SyntaxParsers/WithParser.ts
@@ -1,24 +1,58 @@
-import { RegexParser, IPrimitiveExpression } from '../Parser/RegexParser';
+import { RegexParser, IPrimitiveExpression } from '../Parser/Regex/RegexParser';
 import { FunctionParameter } from '@/application/Parser/Script/Compiler/Function/Parameter/FunctionParameter';
+import { ExpressionRegexBuilder } from '../Parser/Regex/ExpressionRegexBuilder';

 export class WithParser extends RegexParser {
-    protected readonly regex = /{{\s*with\s+\$([^}| ]+)\s*}}\s*([^)]+?)\s*{{\s*end\s*}}/g;
+    protected readonly regex = new ExpressionRegexBuilder()
+        // {{ with $parameterName }}
+        .expectExpressionStart()
+        .expectCharacters('with')
+        .expectOneOrMoreWhitespaces()
+        .expectCharacters('$')
+        .matchUntilFirstWhitespace()                    // First match: parameter name
+        .expectExpressionEnd()
+        // ...
+        .matchAnythingExceptSurroundingWhitespaces()    // Second match: Scope text
+        // {{ end }}
+        .expectExpressionStart()
+        .expectCharacters('end')
+        .expectExpressionEnd()
+        .buildRegExp();
+
    protected buildExpression(match: RegExpMatchArray): IPrimitiveExpression {
        const parameterName = match[1];
-        const innerText = match[2];
+        const scopeText = match[2];
        return {
            parameters: [ new FunctionParameter(parameterName, true) ],
-            evaluator: (args) => {
-                const argumentValue = args.hasArgument(parameterName) ?
-                    args.getArgument(parameterName).argumentValue
+            evaluator: (context) => {
+                const argumentValue = context.args.hasArgument(parameterName) ?
+                    context.args.getArgument(parameterName).argumentValue
                    : undefined;
                if (!argumentValue) {
                    return '';
                }
-                const substitutionRegex = /{{\s*.\s*}}/g;
-                const newText = innerText.replace(substitutionRegex, argumentValue);
-                return newText;
+                return replaceEachScopeSubstitution(scopeText, (pipeline) => {
+                    if (!pipeline) {
+                        return argumentValue;
+                    }
+                    return context.pipelineCompiler.compile(argumentValue, pipeline);
+                });
            },
        };
    }
 }
+
+const ScopeSubstitutionRegEx = new ExpressionRegexBuilder()
+    // {{ . | pipeName }}
+    .expectExpressionStart()
+    .expectCharacters('.')
+    .matchPipeline()    // First match: pipeline
+    .expectExpressionEnd()
+    .buildRegExp();
+
+function replaceEachScopeSubstitution(scopeText: string, replacer: (pipeline: string) => string) {
+    // Not using /{{\s*.\s*(?:(\|\s*[^{}]*?)\s*)?}}/g for not matching brackets, but let pipeline compiler fail on those
+    return scopeText.replaceAll(ScopeSubstitutionRegEx, (_$, match1 ) => {
+        return replacer(match1);
+    });
+}
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/Expression/Expression.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/Expression/Expression.spec.ts
@@ -1,13 +1,16 @@
 import 'mocha';
 import { expect } from 'chai';
 import { ExpressionPosition } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionPosition';
-import { ExpressionEvaluator } from '@/application/Parser/Script/Compiler/Expressions/Expression/Expression';
-import { Expression } from '@/application/Parser/Script/Compiler/Expressions/Expression/Expression';
-import { IReadOnlyFunctionParameterCollection } from '@/application/Parser/Script/Compiler/Function/Parameter/IFunctionParameterCollection';
+// tslint:disable-next-line:max-line-length
+import { ExpressionEvaluator, Expression } from '@/application/Parser/Script/Compiler/Expressions/Expression/Expression';
 import { IReadOnlyFunctionCallArgumentCollection } from '@/application/Parser/Script/Compiler/FunctionCall/Argument/IFunctionCallArgumentCollection';
 import { FunctionCallArgumentCollectionStub } from '@tests/unit/stubs/FunctionCallArgumentCollectionStub';
 import { FunctionParameterCollectionStub } from '@tests/unit/stubs/FunctionParameterCollectionStub';
 import { FunctionCallArgumentStub } from '@tests/unit/stubs/FunctionCallArgumentStub';
+import { ExpressionEvaluationContextStub } from '@tests/unit/stubs/ExpressionEvaluationContextStub';
+import { IPipelineCompiler } from '@/application/Parser/Script/Compiler/Expressions/Pipes/IPipelineCompiler';
+import { PipelineCompilerStub } from '@tests/unit/stubs/PipelineCompilerStub';
+import { IReadOnlyFunctionParameterCollection } from '@/application/Parser/Script/Compiler/Function/Parameter/IFunctionParameterCollection';

 describe('Expression', () => {
    describe('ctor', () => {
@@ -79,19 +82,21 @@ describe('Expression', () => {
            const testCases = [
                {
                    name: 'throws if arguments is undefined',
-                    args: undefined,
-                    expectedError: 'undefined args, send empty collection instead',
+                    context: undefined,
+                    expectedError: 'undefined context',
                },
                {
                    name: 'throws when some of the required args are not provided',
                    sut: (i: ExpressionBuilder) => i.withParameterNames(['a', 'b', 'c'], false),
-                    args: new FunctionCallArgumentCollectionStub().withArgument('b', 'provided'),
+                    context: new ExpressionEvaluationContextStub()
+                        .withArgs(new FunctionCallArgumentCollectionStub().withArgument('b', 'provided')),
                    expectedError: 'argument values are provided for required parameters: "a", "c"',
                },
                {
                    name: 'throws when none of the required args are not provided',
                    sut: (i: ExpressionBuilder) => i.withParameterNames(['a', 'b'], false),
-                    args: new FunctionCallArgumentCollectionStub().withArgument('c', 'unrelated'),
+                    context: new ExpressionEvaluationContextStub()
+                        .withArgs(new FunctionCallArgumentCollectionStub().withArgument('c', 'unrelated')),
                    expectedError: 'argument values are provided for required parameters: "a", "b"',
                },
            ];
@@ -104,7 +109,7 @@ describe('Expression', () => {
                    }
                    const sut = sutBuilder.build();
                    // act
-                    const act = () => sut.evaluate(testCase.args);
+                    const act = () => sut.evaluate(testCase.context);
                    // assert
                    expect(act).to.throw(testCase.expectedError);
                });
@@ -112,29 +117,50 @@ describe('Expression', () => {
        });
        it('returns result from evaluator', () => {
            // arrange
-            const evaluatorMock: ExpressionEvaluator = (args) =>
-                `"${args
+            const evaluatorMock: ExpressionEvaluator = (c) =>
+                `"${c
+                    .args
                    .getAllParameterNames()
-                    .map((name) => args.getArgument(name))
+                    .map((name) => context.args.getArgument(name))
                    .map((arg) => `${arg.parameterName}': '${arg.argumentValue}'`)
                    .join('", "')}"`;
            const givenArguments = new FunctionCallArgumentCollectionStub()
                .withArgument('parameter1', 'value1')
                .withArgument('parameter2', 'value2');
            const expectedParameterNames = givenArguments.getAllParameterNames();
-            const expected = evaluatorMock(givenArguments);
+            const context = new ExpressionEvaluationContextStub()
+                    .withArgs(givenArguments);
+            const expected = evaluatorMock(context);
            const sut = new ExpressionBuilder()
                .withEvaluator(evaluatorMock)
                .withParameterNames(expectedParameterNames)
                .build();
            // arrange
-            const actual = sut.evaluate(givenArguments);
+            const actual = sut.evaluate(context);
            // assert
            expect(expected).to.equal(actual,
                `\nGiven arguments: ${JSON.stringify(givenArguments)}\n` +
                `\nExpected parameter names: ${JSON.stringify(expectedParameterNames)}\n`,
            );
        });
+        it('sends pipeline compiler as it is', () => {
+            // arrange
+            const expected = new PipelineCompilerStub();
+            const context = new ExpressionEvaluationContextStub()
+                .withPipelineCompiler(expected);
+            let actual: IPipelineCompiler;
+            const evaluatorMock: ExpressionEvaluator = (c) => {
+                actual = c.pipelineCompiler;
+                return '';
+            };
+            const sut = new ExpressionBuilder()
+                .withEvaluator(evaluatorMock)
+                .build();
+            // arrange
+            sut.evaluate(context);
+            // assert
+            expect(expected).to.equal(actual);
+        });
        describe('filters unused parameters', () => {
            // arrange
            const testCases = [
@@ -166,16 +192,18 @@ describe('Expression', () => {
            for (const testCase of testCases) {
                it(testCase.name, () => {
                    let actual: IReadOnlyFunctionCallArgumentCollection;
-                    const evaluatorMock: ExpressionEvaluator = (providedArgs) => {
-                        actual = providedArgs;
+                    const evaluatorMock: ExpressionEvaluator = (c) => {
+                        actual = c.args;
                        return '';
                    };
+                    const context = new ExpressionEvaluationContextStub()
+                        .withArgs(testCase.arguments);
                    const sut = new ExpressionBuilder()
                        .withEvaluator(evaluatorMock)
                        .withParameters(testCase.expressionParameters)
                        .build();
                    // act
-                    sut.evaluate(testCase.arguments);
+                    sut.evaluate(context);
                    // assert
                    const actualArguments = actual.getAllParameterNames().map((name) => actual.getArgument(name));
                    expect(actualArguments).to.deep.equal(testCase.expectedArguments);
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext.spec.ts
@@ -0,0 +1,65 @@
+import 'mocha';
+import { expect } from 'chai';
+import { ExpressionEvaluationContext, IExpressionEvaluationContext } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext';
+import { IReadOnlyFunctionCallArgumentCollection } from '@/application/Parser/Script/Compiler/FunctionCall/Argument/IFunctionCallArgumentCollection';
+import { IPipelineCompiler } from '@/application/Parser/Script/Compiler/Expressions/Pipes/IPipelineCompiler';
+import { FunctionCallArgumentCollectionStub } from '@tests/unit/stubs/FunctionCallArgumentCollectionStub';
+import { PipelineCompilerStub } from '@tests/unit/stubs/PipelineCompilerStub';
+
+
+describe('ExpressionEvaluationContext', () => {
+    describe('ctor', () => {
+        describe('args', () => {
+            it('throws if args are undefined', () => {
+                // arrange
+                const expectedError = 'undefined args';
+                const builder = new ExpressionEvaluationContextBuilder()
+                    .withArgs(undefined);
+                // act
+                const act = () => builder.build();
+                // assert
+                expect(act).throw(expectedError);
+            });
+            it('sets as expected', () => {
+                // arrange
+                const expected = new FunctionCallArgumentCollectionStub()
+                    .withArgument('expectedParameter', 'expectedValue');
+                const builder = new ExpressionEvaluationContextBuilder()
+                    .withArgs(expected);
+                // act
+                const sut = builder.build();
+                // assert
+                const actual = sut.args;
+                expect(actual).to.equal(expected);
+            });
+        });
+        describe('pipelineCompiler', () => {
+            it('sets as expected', () => {
+                // arrange
+                const expected = new PipelineCompilerStub();
+                const builder = new ExpressionEvaluationContextBuilder()
+                    .withPipelineCompiler(expected);
+                // act
+                const sut = builder.build();
+                // assert
+                expect(sut.pipelineCompiler).to.equal(expected);
+            });
+        });
+    });
+});
+
+class ExpressionEvaluationContextBuilder {
+    private args: IReadOnlyFunctionCallArgumentCollection = new FunctionCallArgumentCollectionStub();
+    private pipelineCompiler: IPipelineCompiler = new PipelineCompilerStub();
+    public withArgs(args: IReadOnlyFunctionCallArgumentCollection) {
+        this.args = args;
+        return this;
+    }
+    public withPipelineCompiler(pipelineCompiler: IPipelineCompiler) {
+        this.pipelineCompiler = pipelineCompiler;
+        return this;
+    }
+    public build(): IExpressionEvaluationContext {
+        return new ExpressionEvaluationContext(this.args, this.pipelineCompiler);
+    }
+}
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/ExpressionsCompiler.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/ExpressionsCompiler.spec.ts
@@ -74,9 +74,9 @@ describe('ExpressionsCompiler', () => {
                sut.compileExpressions(code, expected);
                // assert
                expect(expressions[0].callHistory).to.have.lengthOf(1);
-                expect(expressions[0].callHistory[0]).to.equal(expected);
+                expect(expressions[0].callHistory[0].args).to.equal(expected);
                expect(expressions[1].callHistory).to.have.lengthOf(1);
-                expect(expressions[1].callHistory[0]).to.equal(expected);
+                expect(expressions[1].callHistory[0].args).to.equal(expected);
            });
            it('throws if arguments is undefined', () => {
                // arrange
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/Parser/Regex/ExpressionRegexBuilder.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/Parser/Regex/ExpressionRegexBuilder.spec.ts
@@ -0,0 +1,135 @@
+import 'mocha';
+import { expect } from 'chai';
+import { ExpressionRegexBuilder } from '@/application/Parser/Script/Compiler/Expressions/Parser/Regex/ExpressionRegexBuilder';
+
+describe('ExpressionRegexBuilder', () => {
+    describe('expectCharacters', () => {
+        describe('escape single as expected', () => {
+            const charactersToEscape = [ '.', '$' ];
+            for (const character of charactersToEscape) {
+                it(character, () => {
+                    runRegExTest(
+                        // act
+                        (act) => act.expectCharacters(character),
+                        // assert
+                        `\\${character}`);
+                });
+            }
+        });
+        it('escapes multiple as expected', () => {
+            runRegExTest(
+                // act
+                (act) => act.expectCharacters('.I have no $$.'),
+                // assert
+                '\\.I have no \\$\\\$\\.');
+        });
+        it('adds as expected', () => {
+            runRegExTest(
+                // act
+                (act) => act.expectCharacters('return as it is'),
+                // assert
+                'return as it is');
+        });
+    });
+    it('expectOneOrMoreWhitespaces', () => {
+        runRegExTest(
+            // act
+            (act) => act.expectOneOrMoreWhitespaces(),
+            // assert
+            '\\s+');
+    });
+    it('matchPipeline', () => {
+        runRegExTest(
+            // act
+            (act) => act.matchPipeline(),
+            // assert
+            '\\s*(\\|\\s*.+?)?');
+    });
+    it('matchUntilFirstWhitespace', () => {
+        runRegExTest(
+            // act
+            (act) => act.matchUntilFirstWhitespace(),
+            // assert
+            '([^|\\s]+)');
+    });
+    it('matchAnythingExceptSurroundingWhitespaces', () => {
+        runRegExTest(
+            // act
+            (act) => act.matchAnythingExceptSurroundingWhitespaces(),
+            // assert
+            '\\s*(.+?)\\s*');
+    });
+    it('expectExpressionStart', () => {
+        runRegExTest(
+            // act
+            (act) => act.expectExpressionStart(),
+            // assert
+            '{{\\s*');
+    });
+    it('expectExpressionEnd', () => {
+        runRegExTest(
+            // act
+            (act) => act.expectExpressionEnd(),
+            // assert
+            '\\s*}}');
+    });
+    describe('buildRegExp', () => {
+        it('sets global flag', () => {
+            // arrange
+            const expected = 'g';
+            const sut = new ExpressionRegexBuilder()
+                .expectOneOrMoreWhitespaces();
+            // act
+            const actual = sut.buildRegExp().flags;
+            // assert
+            expect(actual).to.equal(expected);
+        });
+        describe('can combine multiple parts', () => {
+            it('with', () => {
+                runRegExTest((sut) => sut
+                    // act
+                    .expectExpressionStart().expectCharacters('with').expectOneOrMoreWhitespaces().expectCharacters('$')
+                    .matchUntilFirstWhitespace()
+                    .expectExpressionEnd()
+                    .matchAnythingExceptSurroundingWhitespaces()
+                    .expectExpressionStart().expectCharacters('end').expectExpressionEnd(),
+                    // assert
+                    '{{\\s*with\\s+\\$([^|\\s]+)\\s*}}\\s*(.+?)\\s*{{\\s*end\\s*}}',
+                );
+            });
+            it('scoped substitution', () => {
+                runRegExTest((sut) => sut
+                    // act
+                    .expectExpressionStart().expectCharacters('.')
+                    .matchPipeline()
+                    .expectExpressionEnd(),
+                    // assert
+                    '{{\\s*\\.\\s*(\\|\\s*.+?)?\\s*}}',
+                );
+            });
+            it('parameter substitution', () => {
+                runRegExTest((sut) => sut
+                    // act
+                    .expectExpressionStart().expectCharacters('$')
+                    .matchUntilFirstWhitespace()
+                    .matchPipeline()
+                    .expectExpressionEnd(),
+                    // assert
+                    '{{\\s*\\$([^|\\s]+)\\s*(\\|\\s*.+?)?\\s*}}',
+                );
+            });
+        });
+    });
+});
+
+function runRegExTest(
+    act: (sut: ExpressionRegexBuilder) => ExpressionRegexBuilder,
+    expected: string,
+    ) {
+    // arrange
+    const sut = new ExpressionRegexBuilder();
+    // act
+    const actual = act(sut).buildRegExp().source;
+    // assert
+    expect(actual).to.equal(expected);
+}
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser.spec.ts
@@ -1,7 +1,7 @@
 import 'mocha';
 import { expect } from 'chai';
 import { ExpressionEvaluator } from '@/application/Parser/Script/Compiler/Expressions/Expression/Expression';
-import { IPrimitiveExpression, RegexParser } from '@/application/Parser/Script/Compiler/Expressions/Parser/RegexParser';
+import { IPrimitiveExpression, RegexParser } from '@/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser';
 import { ExpressionPosition } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionPosition';
 import { FunctionParameterStub } from '@tests/unit/stubs/FunctionParameterStub';

--- a/tests/unit/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory.spec.ts
@@ -0,0 +1,113 @@
+import 'mocha';
+import { expect } from 'chai';
+import { PipeFactory } from '@/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory';
+import { PipeStub } from '@tests/unit/stubs/PipeStub';
+
+describe('PipeFactory', () => {
+    describe('ctor', () => {
+        it('throws when instances with same name is registered', () => {
+            // arrange
+            const duplicateName = 'duplicateName';
+            const expectedError = `Pipe name must be unique: "${duplicateName}"`;
+            const pipes = [
+                new PipeStub().withName(duplicateName),
+                new PipeStub().withName('uniqueName'),
+                new PipeStub().withName(duplicateName),
+            ];
+            // act
+            const act = () => new PipeFactory(pipes);
+            // expect
+            expect(act).to.throw(expectedError);
+        });
+        it('throws when a pipe is undefined', () => {
+            // arrange
+            const expectedError = 'undefined pipe in list';
+            const pipes = [ new PipeStub(), undefined ];
+            // act
+            const act = () => new PipeFactory(pipes);
+            // expect
+            expect(act).to.throw(expectedError);
+        });
+        describe('throws when name is invalid', () => {
+            // act
+            const act = (invalidName: string) => new PipeFactory([ new PipeStub().withName(invalidName) ]);
+            // assert
+            testPipeNameValidation(act);
+        });
+    });
+    describe('get', () => {
+        describe('throws when name is invalid', () => {
+            // arrange
+            const sut = new PipeFactory();
+            // act
+            const act = (invalidName: string) => sut.get(invalidName);
+            // assert
+            testPipeNameValidation(act);
+        });
+        it('gets registered instance when it exists', () => {
+            // arrange
+            const expected = new PipeStub().withName('expectedName');
+            const pipes = [ expected, new PipeStub().withName('instanceToConfuse') ];
+            const sut = new PipeFactory(pipes);
+            // act
+            const actual = sut.get(expected.name);
+            // expect
+            expect(actual).to.equal(expected);
+        });
+        it('throws when instance does not exist', () => {
+            // arrange
+            const missingName = 'missingName';
+            const expectedError = `Unknown pipe: "${missingName}"`;
+            const pipes = [ ];
+            const sut = new PipeFactory(pipes);
+            // act
+            const act = () => sut.get(missingName);
+            // expect
+            expect(act).to.throw(expectedError);
+        });
+    });
+});
+
+function testPipeNameValidation(testRunner: (invalidName: string) => void) {
+    const testCases = [
+        {
+            exceptionBuilder: () => 'empty pipe name',
+            values: [ null, undefined , ''],
+        },
+        {
+            exceptionBuilder: (name: string) => `Pipe name should be camelCase: "${name}"`,
+            values: [
+                'PascalCase',
+                'snake-case',
+                'includesNumb3rs',
+                'includes Whitespace',
+                'noSpec\'ial',
+            ],
+        },
+    ];
+    for (const testCase of testCases) {
+        for (const invalidName of testCase.values) {
+            it(`invalid name (${printValue(invalidName)}) throws`, () => {
+                // arrange
+                const expectedError = testCase.exceptionBuilder(invalidName);
+                // act
+                const act = () => testRunner(invalidName);
+                // expect
+                expect(act).to.throw(expectedError);
+            });
+        }
+    }
+}
+
+function printValue(value: string) {
+    switch (value) {
+        case undefined:
+            return 'undefined';
+        case null:
+            return 'null';
+        case '':
+            return 'empty';
+        default:
+            return value;
+    }
+}
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/Pipes/PipelineCompiler.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/Pipes/PipelineCompiler.spec.ts
@@ -0,0 +1,138 @@
+import 'mocha';
+import { expect } from 'chai';
+import { PipelineCompiler } from '@/application/Parser/Script/Compiler/Expressions/Pipes/PipelineCompiler';
+import { IPipelineCompiler } from '@/application/Parser/Script/Compiler/Expressions/Pipes/IPipelineCompiler';
+import { IPipeFactory } from '@/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory';
+import { PipeStub } from '@tests/unit/stubs/PipeStub';
+import { PipeFactoryStub } from '@tests/unit/stubs/PipeFactoryStub';
+
+describe('PipelineCompiler', () => {
+    describe('compile', () => {
+        describe('throws for invalid arguments', () => {
+            interface ITestCase {
+                name: string;
+                act: (test: PipelineTestRunner) => PipelineTestRunner;
+                expectedError: string;
+            }
+            const testCases: ITestCase[] = [
+                {
+                    name: '"value" is empty',
+                    act: (test) => test.withValue(''),
+                    expectedError: 'undefined value',
+                },
+                {
+                    name: '"value" is undefined',
+                    act: (test) => test.withValue(undefined),
+                    expectedError: 'undefined value',
+                },
+                {
+                    name: '"pipeline" is empty',
+                    act: (test) => test.withPipeline(''),
+                    expectedError: 'undefined pipeline',
+                },
+                {
+                    name: '"pipeline" is undefined',
+                    act: (test) => test.withPipeline(undefined),
+                    expectedError: 'undefined pipeline',
+                },
+                {
+                    name: '"pipeline" does not start with pipe',
+                    act: (test) => test.withPipeline('pipeline |'),
+                    expectedError: 'pipeline does not start with pipe',
+                },
+            ];
+            for (const testCase of testCases) {
+                it(testCase.name, () => {
+                    // act
+                    const runner = new PipelineTestRunner();
+                    testCase.act(runner);
+                    const act = () => runner.compile();
+                    // assert
+                    expect(act).to.throw(testCase.expectedError);
+                });
+            }
+        });
+        describe('compiles pipeline as expected', () => {
+            const testCases = [
+                {
+                    name: 'compiles single pipe as expected',
+                    pipes: [
+                        new PipeStub().withName('doublePrint').withApplier((value) => `${value}-${value}`),
+                    ],
+                    pipeline: '| doublePrint',
+                    value: 'value',
+                    expected: 'value-value',
+                },
+                {
+                    name: 'compiles multiple pipes as expected',
+                    pipes: [
+                        new PipeStub().withName('prependLetterA').withApplier((value) => `A-${value}`),
+                        new PipeStub().withName('prependLetterB').withApplier((value) => `B-${value}`),
+                    ],
+                    pipeline: '| prependLetterA | prependLetterB',
+                    value: 'value',
+                    expected: 'B-A-value',
+                },
+                {
+                    name: 'compiles with relaxed whitespace placing',
+                    pipes: [
+                        new PipeStub().withName('appendNumberOne').withApplier((value) => `${value}1`),
+                        new PipeStub().withName('appendNumberTwo').withApplier((value) => `${value}2`),
+                        new PipeStub().withName('appendNumberThree').withApplier((value) => `${value}3`),
+                    ],
+                    pipeline: ' |      appendNumberOne|appendNumberTwo|   appendNumberThree',
+                    value: 'value',
+                    expected: 'value123',
+                },
+                {
+                    name: 'can reuse same pipe',
+                    pipes: [
+                        new PipeStub().withName('removeFirstChar').withApplier((value) => `${value.slice(1)}`),
+                    ],
+                    pipeline: ' | removeFirstChar | removeFirstChar | removeFirstChar',
+                    value: 'value',
+                    expected: 'ue',
+                },
+            ];
+            for (const testCase of testCases) {
+                it(testCase.name, () => {
+                    // arrange
+                    const runner =
+                        new PipelineTestRunner()
+                            .withValue(testCase.value)
+                            .withPipeline(testCase.pipeline)
+                            .withFactory(new PipeFactoryStub().withPipes(testCase.pipes));
+                    // act
+                    const actual = runner.compile();
+                    // expect
+                    expect(actual).to.equal(testCase.expected);
+                });
+            }
+        });
+    });
+});
+
+
+class PipelineTestRunner implements IPipelineCompiler {
+    private value: string = 'non-empty-value';
+    private pipeline: string = '| validPipeline';
+    private factory: IPipeFactory = new PipeFactoryStub();
+
+    public withValue(value: string) {
+        this.value = value;
+        return this;
+    }
+    public withPipeline(pipeline: string) {
+        this.pipeline = pipeline;
+        return this;
+    }
+    public withFactory(factory: IPipeFactory) {
+        this.factory = factory;
+        return this;
+    }
+
+    public compile(): string {
+        const sut = new PipelineCompiler(this.factory);
+        return sut.compile(this.value, this.pipeline);
+    }
+}
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/SyntaxParsers/ParameterSubstitutionParser.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/SyntaxParsers/ParameterSubstitutionParser.spec.ts
@@ -57,4 +57,11 @@ describe('ParameterSubstitutionParser', () => {
            },
        );
    });
+    describe('compiles pipes as expected', () => {
+        runner.expectPipeHits({
+            codeBuilder: (pipeline) => `{{ $argument${pipeline}}}`,
+            parameterName: 'argument',
+            parameterValue: 'value',
+        });
+    });
 });
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/SyntaxParsers/SyntaxParserTestsRunner.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/SyntaxParsers/SyntaxParserTestsRunner.ts
@@ -3,6 +3,8 @@ import { expect } from 'chai';
 import { ExpressionPosition } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionPosition';
 import { IExpressionParser } from '@/application/Parser/Script/Compiler/Expressions/Parser/IExpressionParser';
 import { FunctionCallArgumentCollectionStub } from '@tests/unit/stubs/FunctionCallArgumentCollectionStub';
+import { ExpressionEvaluationContextStub } from '@tests/unit/stubs/ExpressionEvaluationContextStub';
+import { PipelineCompilerStub } from '@tests/unit/stubs/PipelineCompilerStub';

 export class SyntaxParserTestsRunner {
    constructor(private readonly sut: IExpressionParser) {
@@ -24,17 +26,66 @@ export class SyntaxParserTestsRunner {
            it(testCase.name, () => {
                // arrange
                const args = testCase.args(new FunctionCallArgumentCollectionStub());
+                const context = new ExpressionEvaluationContextStub()
+                    .withArgs(args);
                // act
                const expressions = this.sut.findExpressions(testCase.code);
                // assert
-                const actual = expressions.map((e) => e.evaluate(args));
+                const actual = expressions.map((e) => e.evaluate(context));
                expect(actual).to.deep.equal(testCase.expected);
            });
        }
        return this;
    }
+    public expectPipeHits(data: IExpectPipeHitTestData) {
+        for (const validPipePart of PipeTestCases.ValidValues) {
+            this.expectHitPipePart(validPipePart, data);
+        }
+        for (const invalidPipePart of PipeTestCases.InvalidValues) {
+            this.expectMissPipePart(invalidPipePart, data);
+        }
+    }
+    private expectHitPipePart(pipeline: string, data: IExpectPipeHitTestData) {
+        it(`"${pipeline}" hits`, () => {
+            // arrange
+            const expectedPipePart = pipeline.trim();
+            const code = data.codeBuilder(pipeline);
+            const args = new FunctionCallArgumentCollectionStub()
+                .withArgument(data.parameterName, data.parameterValue);
+            const pipelineCompiler = new PipelineCompilerStub();
+            const context = new ExpressionEvaluationContextStub()
+                .withPipelineCompiler(pipelineCompiler)
+                .withArgs(args);
+            // act
+            const expressions = this.sut.findExpressions(code);
+            expressions[0].evaluate(context);
+            // assert
+            expect(expressions).has.lengthOf(1);
+            expect(pipelineCompiler.compileHistory).has.lengthOf(1);
+            const actualPipeNames = pipelineCompiler.compileHistory[0].pipeline;
+            const actualValue = pipelineCompiler.compileHistory[0].value;
+            expect(actualPipeNames).to.equal(expectedPipePart);
+            expect(actualValue).to.equal(data.parameterValue);
+        });
+    }
+    private expectMissPipePart(pipeline: string, data: IExpectPipeHitTestData) {
+        it(`"${pipeline}" misses`, () => {
+            // arrange
+            const args = new FunctionCallArgumentCollectionStub()
+                .withArgument(data.parameterName, data.parameterValue);
+            const pipelineCompiler = new PipelineCompilerStub();
+            const context = new ExpressionEvaluationContextStub()
+                .withPipelineCompiler(pipelineCompiler)
+                .withArgs(args);
+            const code = data.codeBuilder(pipeline);
+            // act
+            const expressions = this.sut.findExpressions(code);
+            expressions[0]?.evaluate(context); // Because an expression may include another with pipes
+            // assert
+            expect(pipelineCompiler.compileHistory).has.lengthOf(0);
+        });
+    }
 }
-
 interface IExpectResultTestCase {
    name: string;
    code: string;
@@ -47,3 +98,25 @@ interface IExpectPositionTestCase {
    code: string;
    expected: readonly ExpressionPosition[];
 }
+
+interface IExpectPipeHitTestData {
+    codeBuilder: (pipeline: string) => string;
+    parameterName: string;
+    parameterValue: string;
+}
+
+const PipeTestCases = {
+    ValidValues: [
+        // Single pipe with different whitespace combinations
+        ' | pipe1', ' |pipe1', '|pipe1', ' |pipe1', '   |   pipe1',
+
+        // Double pipes with different whitespace combinations
+        ' | pipe1 | pipe2', '| pipe1|pipe2', '|pipe1|pipe2', ' |pipe1 |pipe2', '| pipe1 | pipe2| pipe3 |pipe4',
+
+        // Wrong cases, but should match anyway and let pipelineCompiler throw errors
+        '| pip€', '| pip{e} ',
+    ],
+    InvalidValues: [
+        ' pipe1  |pipe2', ' pipe1',
+    ],
+};
--- a/tests/unit/application/Parser/Script/Compiler/Expressions/SyntaxParsers/WithParser.spec.ts
+++ b/tests/unit/application/Parser/Script/Compiler/Expressions/SyntaxParsers/WithParser.spec.ts
@@ -17,7 +17,7 @@ describe('WithParser', () => {
            {
                name: 'when scope is used',
                code: 'used here ({{ with $parameter }}value: {{.}}{{ end }})',
-                expected: [ new ExpressionPosition(11, 55) ],
+                expected: [ new ExpressionPosition(11, 53) ],
            },
            {
                name: 'when used twice',
@@ -25,18 +25,14 @@ describe('WithParser', () => {
                expected: [ new ExpressionPosition(7, 51), new ExpressionPosition(61, 99) ],
            },
            {
-                name: 'tolerates lack of spaces around brackets',
+                name: 'tolerate lack of whitespaces',
                code: 'no whitespaces {{with $parameter}}value: {{ . }}{{end}}',
-                expected: [ new ExpressionPosition(15, 53) ],
-            },
-            {
-                name: 'does not tolerate space after dollar sign',
-                code: 'used here ({{ with $ parameter }}value: {{ . }}{{ end }})',
-                expected: [ ],
+                expected: [ new ExpressionPosition(15, 55) ],
            },
        );
    });
-    describe('ignores when syntax is unexpected', () => {
+    describe('ignores when syntax is wrong', () => {
+        describe('ignores expression if "with" syntax is wrong', () => {
            runner.expectPosition(
                {
                    name: 'does not tolerate whitespace after with',
@@ -48,7 +44,102 @@ describe('WithParser', () => {
                    code: '{{ with$parameter}}value: {{ . }}{{ end }}',
                    expected: [ ],
                },
+                {
+                    name: 'wrong text at scope end',
+                    code: '{{ with$parameter}}value: {{ . }}{{ fin }}',
+                    expected: [ ],
+                },
+                {
+                    name: 'wrong text at expression start',
+                    code: '{{ when $parameter}}value: {{ . }}{{ end }}',
+                    expected: [ ],
+                },
            );
+
+        });
+        describe('does not render argument if substitution syntax is wrong', () => {
+            runner.expectResults(
+                {
+                    name: 'comma used instead of dot',
+                    code: '{{ with $parameter }}Hello {{ , }}{{ end }}',
+                    args: (args) => args
+                        .withArgument('parameter', 'world!'),
+                    expected: [ 'Hello {{ , }}' ],
+                },
+                {
+                    name: 'single brackets instead of double',
+                    code: '{{ with $parameter }}Hello { . }{{ end }}',
+                    args: (args) => args
+                        .withArgument('parameter', 'world!'),
+                    expected: [ 'Hello { . }' ],
+                },
+                {
+                    name: 'double dots instead of single',
+                    code: '{{ with $parameter }}Hello {{ .. }}{{ end }}',
+                    args: (args) => args
+                        .withArgument('parameter', 'world!'),
+                    expected: [ 'Hello {{ .. }}' ],
+                },
+            );
+        });
+    });
+    describe('renders scope conditionally', () => {
+        describe('does not render scope if argument is undefined', () => {
+            runner.expectResults(
+                {
+                    name: 'does not render when value is undefined',
+                    code: '{{ with $parameter }}dark{{ end }} ',
+                    args: (args) => args
+                        .withArgument('parameter', undefined),
+                    expected: [ '' ],
+                },
+                {
+                    name: 'does not render when value is empty',
+                    code: '{{ with $parameter }}dark {{.}}{{ end }}',
+                    args: (args) => args
+                        .withArgument('parameter', ''),
+                    expected: [ '' ],
+                },
+                {
+                    name: 'does not render when argument is not provided',
+                    code: '{{ with $parameter }}dark{{ end }}',
+                    args: (args) => args,
+                    expected: [ '' ],
+                },
+            );
+        });
+        describe('render scope when variable has value', () => {
+            runner.expectResults(
+                {
+                    name: 'renders scope even if value is not used',
+                    code: '{{ with $parameter }}Hello world!{{ end }}',
+                    args: (args) => args
+                        .withArgument('parameter', 'Hello'),
+                    expected: [ 'Hello world!' ],
+                },
+                {
+                    name: 'renders value when it has value',
+                    code: '{{ with $parameter }}{{ . }} world!{{ end }}',
+                    args: (args) => args
+                        .withArgument('parameter', 'Hello'),
+                    expected: [ 'Hello world!' ],
+                },
+                {
+                    name: 'renders value when whitespaces around brackets are missing',
+                    code: '{{ with $parameter }}{{.}} world!{{ end }}',
+                    args: (args) => args
+                        .withArgument('parameter', 'Hello'),
+                    expected: [ 'Hello world!' ],
+                },
+                {
+                    name: 'renders value multiple times when it\'s used multiple times',
+                    code: '{{ with $letterL }}He{{ . }}{{ . }}o wor{{ . }}d!{{ end }}',
+                    args: (args) => args
+                        .withArgument('letterL', 'l'),
+                    expected: [ 'Hello world!' ],
+                },
+            );
+        });
    });
    describe('ignores trailing and leading whitespaces and newlines inside scope', () => {
        runner.expectResults(
@@ -82,60 +173,11 @@ describe('WithParser', () => {
            },
        );
    });
-    describe('does not render scope if argument is undefined', () => {
-        runner.expectResults(
-            {
-                name: 'does not render when value is undefined',
-                code: '{{ with $parameter }}dark{{ end }} ',
-                args: (args) => args
-                    .withArgument('parameter', undefined),
-                expected: [ '' ],
-            },
-            {
-                name: 'does not render when value is empty',
-                code: '{{ with $parameter }}dark {{.}}{{ end }}',
-                args: (args) => args
-                    .withArgument('parameter', ''),
-                expected: [ '' ],
-            },
-            {
-                name: 'does not render when argument is not provided',
-                code: '{{ with $parameter }}dark{{ end }}',
-                args: (args) => args,
-                expected: [ '' ],
-            },
-        );
-    });
-    describe('renders scope as expected', () => {
-        runner.expectResults(
-            {
-                name: 'renders scope even if value is not used',
-                code: '{{ with $parameter }}Hello world!{{ end }}',
-                args: (args) => args
-                    .withArgument('parameter', 'Hello'),
-                expected: [ 'Hello world!' ],
-            },
-            {
-                name: 'renders value when it has value',
-                code: '{{ with $parameter }}{{ . }} world!{{ end }}',
-                args: (args) => args
-                    .withArgument('parameter', 'Hello'),
-                expected: [ 'Hello world!' ],
-            },
-            {
-                name: 'renders value when whitespaces around brackets are missing',
-                code: '{{ with $parameter }}{{.}} world!{{ end }}',
-                args: (args) => args
-                    .withArgument('parameter', 'Hello'),
-                expected: [ 'Hello world!' ],
-            },
-            {
-                name: 'renders value multiple times when it\'s used multiple times',
-                code: '{{ with $letterL }}He{{ . }}{{ . }}o wor{{ . }}d!{{ end }}',
-                args: (args) => args
-                    .withArgument('letterL', 'l'),
-                expected: [ 'Hello world!' ],
-            },
-        );
+    describe('compiles pipes in scope as expected', () => {
+        runner.expectPipeHits({
+            codeBuilder: (pipeline) => `{{ with $argument }} {{ .${pipeline}}} {{ end }}`,
+            parameterName: 'argument',
+            parameterValue: 'value',
+        });
    });
 });
--- a/tests/unit/stubs/ExpressionEvaluationContextStub.ts
+++ b/tests/unit/stubs/ExpressionEvaluationContextStub.ts
@@ -0,0 +1,19 @@
+import { IExpressionEvaluationContext } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext';
+import { IPipelineCompiler } from '@/application/Parser/Script/Compiler/Expressions/Pipes/IPipelineCompiler';
+import { IReadOnlyFunctionCallArgumentCollection } from '@/application/Parser/Script/Compiler/FunctionCall/Argument/IFunctionCallArgumentCollection';
+import { FunctionCallArgumentCollectionStub } from './FunctionCallArgumentCollectionStub';
+import { PipelineCompilerStub } from './PipelineCompilerStub';
+
+export class ExpressionEvaluationContextStub implements IExpressionEvaluationContext {
+    public args: IReadOnlyFunctionCallArgumentCollection = new FunctionCallArgumentCollectionStub()
+        .withArgument('test-arg', 'test-value');
+    public pipelineCompiler: IPipelineCompiler = new PipelineCompilerStub();
+    public withArgs(args: IReadOnlyFunctionCallArgumentCollection) {
+        this.args = args;
+        return this;
+    }
+    public withPipelineCompiler(pipelineCompiler: IPipelineCompiler) {
+        this.pipelineCompiler = pipelineCompiler;
+        return this;
+    }
+}
--- a/tests/unit/stubs/ExpressionStub.ts
+++ b/tests/unit/stubs/ExpressionStub.ts
@@ -1,11 +1,11 @@
 import { ExpressionPosition } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionPosition';
 import { IExpression } from '@/application/Parser/Script/Compiler/Expressions/Expression/IExpression';
-import { IReadOnlyFunctionCallArgumentCollection } from '@/application/Parser/Script/Compiler/FunctionCall/Argument/IFunctionCallArgumentCollection';
 import { IReadOnlyFunctionParameterCollection } from '@/application/Parser/Script/Compiler/Function/Parameter/IFunctionParameterCollection';
 import { FunctionParameterCollectionStub } from './FunctionParameterCollectionStub';
+import { IExpressionEvaluationContext } from '@/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext';

 export class ExpressionStub implements IExpression {
-    public callHistory = new Array<IReadOnlyFunctionCallArgumentCollection>();
+    public callHistory = new Array<IExpressionEvaluationContext>();
    public position = new ExpressionPosition(0, 5);
    public parameters: IReadOnlyFunctionParameterCollection = new FunctionParameterCollectionStub();
    private result: string;
@@ -26,8 +26,9 @@ export class ExpressionStub implements IExpression {
        this.result = result;
        return this;
    }
-    public evaluate(args: IReadOnlyFunctionCallArgumentCollection): string {
-        this.callHistory.push(args);
+    public evaluate(context: IExpressionEvaluationContext): string {
+        const args = context.args;
+        this.callHistory.push(context);
        const result = this.result || `[expression-stub] args: ${args ? Object.keys(args).map((key) => `${key}: ${args[key]}`).join('", "') : 'none'}`;
        return result;
    }
--- a/tests/unit/stubs/PipeFactoryStub.ts
+++ b/tests/unit/stubs/PipeFactoryStub.ts
@@ -0,0 +1,28 @@
+import { IPipe } from '@/application/Parser/Script/Compiler/Expressions/Pipes/IPipe';
+import { IPipeFactory } from '@/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory';
+
+export class PipeFactoryStub implements IPipeFactory {
+    private readonly pipes = new Array<IPipe>();
+
+    public get(pipeName: string): IPipe {
+        const result = this.pipes.find((pipe) => pipe.name === pipeName);
+        if (!result) {
+            throw new Error(`pipe not registered: "${pipeName}"`);
+        }
+        return result;
+    }
+
+    public withPipe(pipe: IPipe) {
+        if (!pipe) {
+            throw new Error('undefined pipe');
+        }
+        this.pipes.push(pipe);
+        return this;
+    }
+    public withPipes(pipes: IPipe[]) {
+        for (const pipe of pipes) {
+            this.withPipe(pipe);
+        }
+        return this;
+    }
+}
--- a/tests/unit/stubs/PipeStub.ts
+++ b/tests/unit/stubs/PipeStub.ts
@@ -0,0 +1,16 @@
+import { IPipe } from '@/application/Parser/Script/Compiler/Expressions/Pipes/IPipe';
+
+export class PipeStub implements IPipe {
+    public name: string = 'pipeStub';
+    public apply(raw: string): string {
+        return raw;
+    }
+    public withName(name: string): PipeStub {
+        this.name = name;
+        return this;
+    }
+    public withApplier(applier: (input: string) => string): PipeStub {
+        this.apply = applier;
+        return this;
+    }
+}
--- a/tests/unit/stubs/PipelineCompilerStub.ts
+++ b/tests/unit/stubs/PipelineCompilerStub.ts
@@ -0,0 +1,9 @@
+import { IPipelineCompiler } from '@/application/Parser/Script/Compiler/Expressions/Pipes/IPipelineCompiler';
+
+export class PipelineCompilerStub implements IPipelineCompiler {
+    public compileHistory: Array<{ value: string, pipeline: string }> = [];
+    public compile(value: string, pipeline: string): string {
+        this.compileHistory.push({value, pipeline});
+        return `value: ${value}"\n${pipeline}: ${pipeline}`;
+    }
+}