started tree rewrite

src/BC/Eval.hs

@@ -4,6 +4,29 @@ import BC.Types
 
 eval :: [Value] -> Value
 eval [x@(BInt _)] = x
+eval [x@(BErr _)] = x
 eval [(BOp  x)] = BErr ("operation " ++ x ++ " requires arguments")
-eval (x:xy) = x
 eval [] = BOp ""
+eval l = treeEval l [] []
+
+treeEval :: [Value] -> [Value] -> [Value] -> Value
+treeEval [] [] (num:_) = num
+treeEval [] ops nums = handleOp [] ops nums
+treeEval (x@(BInt _):xy) ops nums = treeEval xy ops (nums ++ [x])
+treeEval expr@(x@(BOp _):xy) ops@(op:_) nums =
+    if precedence x > precedence op
+      then treeEval xy (x:ops) nums
+      else handleOp expr ops nums
+treeEval (x@(BOp _):xy) [] nums = treeEval xy [x] nums
+
+handleOp :: [Value] -> [Value] -> [Value] -> Value
+handleOp expr (op:ops) (op1:(op2:nums)) =
+    treeEval expr ops ((evalOp op op1 op2):nums)
+
+evalOp :: Value -> Value -> Value -> Value
+evalOp (BOp "*") (BInt x) (BInt y) = BInt $ x * y
+evalOp (BOp "/") (BInt x) (BInt y) = BInt $ quot x y
+evalOp (BOp "+") (BInt x) (BInt y) = BInt $ x + y
+evalOp (BOp "-") (BInt x) (BInt y) = BInt $ x - y
+evalOp (BOp "^") (BInt x) (BInt y) = BInt $ x ^ y
+evalOp _ _ _ = BInt 0

src/BC/Types.hs

@@ -11,3 +11,11 @@ instance Show Value where
 isErr :: Value -> Bool
 isErr (BErr _) = True
 isErr _        = False
+
+precedence :: Value -> Int
+precedence (BOp "^") = 1
+precedence (BOp "*") = 2
+precedence (BOp "/") = 2
+precedence (BOp "-") = 1
+precedence (BOp "+") = 1
+precedence _         = 0