From 4fed459d89b6b3abcce8028b19af806b48a38bd7 Mon Sep 17 00:00:00 2001
From: Arnaud Bailly <arnaud@pankzsoft.com>
Date: Sun, 22 Mar 2026 13:16:21 +0100
Subject: Add builtin arithmetic operators
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* also allow choosing evaluator
* ensures equivalence of evaluators up-to α-renaming
* checks server accepts answers from challenge
---
 .../haskell/test/Minilang/Lambda/ParserSpec.hs     | 61 ++++++++++++++++++++++
 1 file changed, 61 insertions(+)

(limited to 'lambda-calcul/haskell/test/Minilang/Lambda/ParserSpec.hs')

diff --git a/lambda-calcul/haskell/test/Minilang/Lambda/ParserSpec.hs b/lambda-calcul/haskell/test/Minilang/Lambda/ParserSpec.hs
index e9cfc6b..08ec661 100644
--- a/lambda-calcul/haskell/test/Minilang/Lambda/ParserSpec.hs
+++ b/lambda-calcul/haskell/test/Minilang/Lambda/ParserSpec.hs
@@ -11,6 +11,7 @@ import qualified Data.Text as Text
 import Minilang.Lambda.Eval (Term (Lam))
 import qualified Minilang.Lambda.Eval as Eval
 import Minilang.Lambda.Parser (AST (..), desugar, initialChars, parse, parseProgram, pretty, restChars)
+import Minilang.Lambda.Eval (normalise)
 import Test.Hspec (Spec, describe, it, parallel, shouldBe, shouldSatisfy)
 import Test.Hspec.QuickCheck (prop)
 import Test.QuickCheck (
@@ -114,6 +115,66 @@ spec = parallel $ do
         let spaced = "- " <> Text.pack (show n)
          in parse spaced `shouldSatisfy` (/= Right (Lit (negate n)))
 
+  describe "arithmetic operators" $ do
+    -- Operator names are valid identifiers: they parse as Sym and round-trip.
+    it "parses + as a symbol" $
+      parse "+" `shouldBe` Right (Sym "+")
+
+    it "parses - as a symbol" $
+      parse "-" `shouldBe` Right (Sym "-")
+
+    it "parses * as a symbol" $
+      parse "*" `shouldBe` Right (Sym "*")
+
+    it "parses div as a symbol" $
+      parse "div" `shouldBe` Right (Sym "div")
+
+    it "parses mod as a symbol" $
+      parse "mod" `shouldBe` Right (Sym "mod")
+
+    it "parses = as a symbol" $
+      parse "=" `shouldBe` Right (Sym "=")
+
+    it "parses < as a symbol" $
+      parse "<" `shouldBe` Right (Sym "<")
+
+    it "parses neg as a symbol" $
+      parse "neg" `shouldBe` Right (Sym "neg")
+
+    -- Full expression parses and round-trips
+    it "parses (+ 3 4) and pretty-prints back" $
+      let expr = App (Sym "+") (Lit 3) [Lit 4]
+       in parse "(+ 3 4)" `shouldBe` Right expr
+
+    it "pretty (+ 3 4) round-trips through parse" $
+      let expr = App (Sym "+") (Lit 3) [Lit 4]
+       in parse (pretty expr) `shouldBe` Right expr
+
+    -- desugar of an arithmetic expression produces a normalised integer
+    it "desugar and normalise (+ 3 4) == Num 7" $
+      normalise (desugar (App (Sym "+") (Lit 3) [Lit 4])) `shouldBe` Eval.Num 7
+
+    it "desugar and normalise (* 2 (+ 1 4)) == Num 10" $
+      normalise (desugar (App (Sym "*") (Lit 2) [App (Sym "+") (Lit 1) [Lit 4]]))
+        `shouldBe` Eval.Num 10
+
+    -- Comparison operators produce Church booleans
+    it "desugar and normalise (= 3 3) == Church True" $
+      normalise (desugar (App (Sym "=") (Lit 3) [Lit 3]))
+        `shouldBe` Eval.Lam "f" (Eval.Lam "t" (Eval.Var "t"))
+
+    it "desugar and normalise (= 3 4) == Church False" $
+      normalise (desugar (App (Sym "=") (Lit 3) [Lit 4]))
+        `shouldBe` Eval.Lam "f" (Eval.Lam "t" (Eval.Var "f"))
+
+    it "desugar and normalise (< 2 5) == Church True" $
+      normalise (desugar (App (Sym "<") (Lit 2) [Lit 5]))
+        `shouldBe` Eval.Lam "f" (Eval.Lam "t" (Eval.Var "t"))
+
+    -- A partial application (missing second arg) pretty-prints as an App
+    it "pretty (+ 1) is \"(+ 1)\"" $
+      pretty (App (Sym "+") (Lit 1) []) `shouldBe` "(+ 1)"
+
   it "parses multiline program with blank lines" $ do
     let program =
           "(def id (lam (x) x))\n\
-- 
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