Language.Haskell.TH.Alpha

Compare TH expressions (or clauses, patterns, etc.) for alpha equivalence. That is, compare for equality modulo the renaming of bound variables.

>>> areExpEq [| \x -> x |] [| \y -> y |]
True

This can be useful when for instance testing libraries that use Template Haskell: usually correctness is only defined up to alpha equivalence.

N.B.: This package doesn't yet handle type annotations correctly!

Documentation

class AlphaEq a where

The main Alpha Equivalence class. @= is by default defined in terms of lkEq. lkEq is exposed for composability: it is easy to recursively build AlphaEq instances from other AlphaEq instances by delegating the lookup update to the subinstances.

Methods

(@=) :: a -> a -> Bool

Compares its arguments for alpha equivalence.

lkEq :: a -> a -> Lookup -> Maybe Lookup

Given a variable binding lookup compares arguments for alpha equivalence, returning Just of updated lookup in case of equivalence, Nothing otherwise.

Instances

AlphaEq DExp

AlphaEq DLetDec

AlphaEq DPat

AlphaEq DType

AlphaEq DKind

AlphaEq DClause

exp_equal :: Quasi m => Exp -> Exp -> m Bool

Compare two expressions for alpha-equivalence. Since this uses th-desugar to desugar the expressions, returns a Bool in the Quasi context.

areExpEq :: Quasi m => ExpQ -> ExpQ -> m Bool