interpreter first version

src/Lox/Interpreter.hs

@@ -0,0 +1,44 @@
+module Lox.Interpreter (
+    eval   
+) where
+
+import Lox.Expr
+import Lox.Scanner
+import Control.Monad.State
+
+data InterpreterState = InterpreterState
+
+eval :: Expr -> Object
+eval expr = evalState (interpret expr) InterpreterState
+
+interpret :: Expr -> State InterpreterState Object
+interpret (Literal value) = return value
+interpret (Grouping expr) = interpret expr
+interpret (Unary op expr) = do 
+    right <- interpret expr
+    case (getType op, right) of
+        (MINUS, NumberObject x) -> return $ NumberObject (-x)
+        (BANG, NullObject) -> return $ BoolObject False
+        (BANG, BoolObject x) -> return $ BoolObject (not x)
+        (BANG, _) -> return $ BoolObject True
+        _ -> error "Type error"
+interpret (Binary leftExpr op rightExpr) = do
+    left <- interpret leftExpr
+    right <- interpret rightExpr
+    case (getType op, left, right) of
+        (PLUS, NumberObject x, NumberObject y) -> return $ NumberObject (x + y)
+        (MINUS, NumberObject x, NumberObject y) -> return $ NumberObject (x - y)
+        (SLASH, NumberObject x, NumberObject y) -> return $ NumberObject (x / y)
+        (STAR, NumberObject x, NumberObject y) -> return $ NumberObject (x * y)
+
+        (GREATER, NumberObject x, NumberObject y) -> return $ BoolObject (x > y)
+        (GREATER_EQUAL, NumberObject x, NumberObject y) -> return $ BoolObject (x >= y)
+        (LESS, NumberObject x, NumberObject y) -> return $ BoolObject (x < y)
+        (LESS_EQUAL, NumberObject x, NumberObject y) -> return $ BoolObject (x <= y)
+
+        (PLUS, StringObject s, StringObject t) -> return $ StringObject (s ++ t)
+
+        (EQUAL_EQUAL, x, y) -> return $ BoolObject (x == y)
+        
+        _ -> error "Type error"
+