DryLisp

A small Lisp interpreter written in Haskell. This was a learning project to understand how parser and interpreters work.

What It Does

DryLisp can evaluate basic Lisp expressions including:

• (1) Atomic expression like numbers, strings, and true/false
• (2) Variables (identifier)
• (3) If statements
• (4) Lambda functions with closures
• (5) Let, let*, and letrec for create a local environment
• (6) Define for naming stuff
• (7) Some build in functions like +, -, *, cons, car, cdr
• (8) Higher-order functions: map, filter, fold, length, append, reverse

Example Usage

1. Use the REPL

cabal run

2. If you want to use it as a module:

import DryLisp
import LispParser

main :: IO ()
main = do
    let input = "(+ 1 2 3)"
    case parse lispExprP input of
        Just (expr, _) -> print $ eval initialEnv expr
        Nothing        -> putStrLn "Parse error"

Closure

Closures capture their environment.

LispClosure
    { closureEnv :: Env
    , closureFn :: [LispExpr] -> Either ErrorMsg (Env, LispExpr) }

The Parser

The parser is built from scratch using applicative functor combinators.

License

GNU GPLv3