Add call-by-name lambda calculus example

sample-programs/lambda_calculus-2.crf

@@ -0,0 +1,53 @@
+data List a where
+    Nil  : List a
+    Cons : a -> List a -> List a
+
+data Pair a b where
+    Pair : a -> b -> Pair a b
+
+data Exp where
+    EVar : Char -> Exp
+    EAbs : Char -> Exp -> Exp
+    EApp : Exp -> Exp -> Exp
+    EInt : Int -> Exp
+    EAdd : Exp -> Exp -> Exp
+
+data Val where
+    VInt     : Int -> Val
+    VClosure : List (Pair Char Val) -> Char -> Exp -> Val
+
+lookup : Char -> List (Pair Char Val) -> Val
+lookup x cxt = case cxt of
+        Cons p ps => case p of
+            Pair y v => case (asciiCode x) == (asciiCode y) of
+                True  => v
+                False => lookup x ps
+
+insert : Char -> Val -> List (Pair Char Val) -> List (Pair Char Val)
+insert x v cxt = Cons (Pair x v) cxt
+
+eval : List (Pair Char Val) -> Exp -> Val
+eval cxt exp = case exp of
+--  EVar x => case lookup x cxt of
+--      VInt i             => VInt i
+--      VClosure delta x e => eval delta e
+    EAbs x e => VClosure cxt x e
+    EApp e1 e2 => case eval cxt e1 of
+        -- FIXME segmentation fault när man löser f istället för 1000
+        VClosure delta x f => eval delta (EInt 1000)
+--  EApp e1 e2 => case eval cxt e1 of
+--      VClosure delta x f => 
+--          let v = VClosure cxt x e2 in
+--          eval (insert x v delta) f
+    EInt i => VInt i
+--  EAdd e1 e2 => 
+--      let i1 = case eval cxt e1 of { VInt i => i } in 
+--      let i2 = case eval cxt e2 of { VInt i => i } in 
+--      VInt (i1 + i2)
+
+exp = EApp (EAbs 'x' (EInt 40)) (EInt 20)
+
+main : Int
+main = case eval Nil exp of
+           VInt i => i
+