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module Evaluation where
import Data.Map as M
import Expr as E
type LabelMap a = Map String a
data Context = Context { variables :: LabelMap Expr
, functions :: LabelMap (String, Expr)
}
eval :: Context -> Expr -> Maybe Expr
eval c (Add e1 e2) = evalInfix c e1 e2 add
eval c (Sub e1 e2) = evalInfix c e1 e2 sub
eval c (Mul e1 e2) = evalInfix c e1 e2 mul
eval c (Div e1 e2) = evalInfix c e1 e2 E.div
eval c (Mod e1 e2) = evalInfix c e1 e2 E.mod
eval c (Exp e1 e2) = evalInfix c e1 e2 E.exp
eval c (Dot e1 e2) = evalInfix c e1 e2 dot
eval c (Variable name) = name `M.lookup` (variables c) >>= eval c
eval (Context vars funcs) (Function name e) =
do arg <- eval (Context vars funcs) e
(argName, functionExpr) <- name `M.lookup` funcs
let localVars = insert argName arg vars
eval (Context localVars funcs) functionExpr
eval c x = Just x
evalInfix :: Context -> Expr -> Expr -> (Expr -> Expr -> Maybe Expr) -> Maybe Expr
evalInfix c e1 e2 f = do a <- eval c e1
b <- eval c e2
f a b
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