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-- | Abstract syntax tree for the untyped lambda calculus, plus some helpers.
module AST (
Expr (..)
) where
-- | Lambda Expressions
data Expr
= Var String
| Lam String Expr
| App Expr Expr
deriving (Eq, Ord)
-- https://www.haskellforall.com/2020/11/pretty-print-syntax-trees-with-this-one.html
showLam, showApp, showVar :: Expr -> String
showLam (Lam i e) = "\\" ++ i ++ " . " ++ showLam e
showLam e = showApp e
showApp (App e1 e2) = showApp e1 ++ " " ++ showVar e2
showApp e = showVar e
showVar (Var i) = i
showVar e = "(" ++ showLam e ++ ")"
instance Show Expr where
show e = showLam e
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