Added semantics for let

Eval.hs

@@ -49,7 +49,7 @@ eval env expr = let (eval', evalFull') = (eval env, evalFull env) in case expr o
 
             Contains -> case args of
                 (mainString:containsWhat:_) -> case (eval' mainString , eval' containsWhat) of
-                    (String a, String b) -> b `sublist` a
+                    (String a, String b) -> Boolean $ b `isSubList` a
 
             Plus -> let (e1:e2:_) = args in case (eval' e1, eval' e2) of
                 (String a, String b) -> String (a ++ b)
@@ -67,25 +67,33 @@ eval env expr = let (eval', evalFull') = (eval env, evalFull env) in case expr o
     (Var name) -> eval' $ findVar env name
 
 
-
+    (Let _ expr) -> expr
 
     
 
-    control@(Control lastResult exprs) -> if null exprs then lastResult else eval' $ evalControl1 env control
+    control@(Control lastResult exprs) -> if null exprs then lastResult else 
+        let (newEnv, newControl) =  evalControl1 env control in
+            eval newEnv newControl
 
     _ -> expr
 
-evalControl1 :: Environment -> Expr -> Expr
-evalControl1 env (Control last (currentExpr:exprs)) = let output = eval env currentExprFull in Control output exprs
-    where 
-        currentExprFull = case currentExpr of
+evalControl1 :: Environment -> Expr -> (Environment, Expr)
+evalControl1 env (Control last (currentExpr:exprs)) = (newEnv, Control newLast exprs)
+    where
+        newLast = eval env $ case currentExpr of
             (FuncCall func [] args) -> FuncCall func [last] args
             _ -> currentExpr
 
+        newEnv = case currentExpr of
+            (Let var expr) -> (var,expr):env
+            _ -> env
+
 evalFull = eval
 --evalFull env (Set xs) = Set (map (eval env) xs) -- evaluates expression fully (not just weak head normal form)
 --evalFull _ e = e
 --TODO implement properly
 concatRecord (Record r1) (Record r2) = Record (r1 ++ r2)
 
-sublist = notImplemented
\ No newline at end of file
+listStartsWith, isSubList :: [a] -> [a] -> Bool
+listStartsWith = notImplemented -- check if first list starts with second list
+isSubList = notImplemented -- check if first list contains second list anywhere in it
\ No newline at end of file

Types.hs

@@ -35,6 +35,7 @@ data Expr = Control Expr [Expr] -- result of last computation, sequence of instr
     | Int Int
     | String String
     | Boolean Bool
+    | Let SymbolName Expr
 --    | Nat Int 
     deriving (Show, Eq)