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Lea

A pipe-oriented functional programming language with a tree-walk interpreter written in TypeScript.

mcclowes/lea
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The Problem​

Functional programming often reads right-to-left or inside-out, making code harder to follow. Chaining transformations requires nested function calls that obscure the data flow.

The Solution​

Lea uses a pipe operator (/>) for left-to-right data flow, making functional composition read naturally like prose. Data flows through transformations in the order you read them.

Key Features​

  • Pipes - Left-to-right data flow using /> operator
  • First-class functions - Optional type annotations
  • Decorators - Function modifiers like #log, #memo, #retry(3)
  • Records - Object literals with member access
  • Contexts - Dependency injection system
  • Async/Await - Promise-based asynchronous execution

Example​

[1, 2, 3, 4, 5]
  /> filter((x) -> x > 2)
  /> map((x) -> x * x)
  /> print

Getting Started​

git clone https://github.com/mcclowes/lea.git
cd lea
npm install
npm run lea example.lea
npm run repl

Architecture​

Source → Lexer → Tokens → Parser → AST → Interpreter → Result

The interpreter follows a traditional pipeline: tokenization, recursive descent parsing, AST representation, and tree-walk interpretation.