module EvaluationSpec (spec) where

import Evaluation (subst)
import Parser (Expr (Abstraction, Application, Variable))
import Test.Hspec

spec :: Spec
spec = do
  describe "subst" $ do
    it "cannot substitute mismatched variables" $
      subst (Variable "x") "y" (Variable "z") `shouldBe` Variable "x"
    it "can substitute matched variables" $
      subst (Variable "x") "x" (Variable "z") `shouldBe` Variable "z"
    it "can substitute nested variables" $
      subst absWithZ "z" absI `shouldNotBe` absWithZMaker absI
  where
    absWithZMaker z = Abstraction "x" (Application z (Variable "x"))
    absWithZ = absWithZMaker (Variable "z")
    absI = Abstraction "i" (Variable "i")