int.icl

   1 implementation module int
   2
   3 import StdEnv
   4 import Data.Either
   5 import Data.Functor
   6 import Data.Maybe
   7 import Data.List
   8 import Control.Applicative
   9 import Control.Monad
  10 import Control.Monad.State
  11 import Control.Monad.Trans
  12
  13 import ast
  14
  15 :: Eval a :== StateT EvalState (Either [String]) a
  16 :: EvalState :== [([Char], Value)]
  17
  18 int :: Expression -> Either [String] Value
  19 int e = evalStateT (eval e) preamble
  20
  21 preamble =
  22         [(['_if'], Func \i->pure (Func \t->pure (Func \e->eval i >>= \(Bool b)->if b (eval t) (eval e))))
  23         ,(['_eq'],  binop \(Int i) (Int j)->Bool (i==j))
  24         ,(['_sub'], binop \(Int i) (Int j)->Int  (i-j))
  25         ,(['_add'], binop \(Int i) (Int j)->Int  (i+j))
  26         ,(['_mul'], binop \(Int i) (Int j)->Int  (i*j))
  27         ,(['_div'], binop \(Int i) (Int j)->Int  (i/j))
  28         ]
  29 where
  30         binop op = Func \l->pure (Func \r->op <$> eval l <*> eval r)
  31
  32 sub :: [Char] Expression Expression -> Expression
  33 sub ident subst (Let v b rest) = Let v (sub ident subst b) (if (v == ident) rest (sub ident subst rest))
  34 sub ident subst (Var v)
  35         | ident == v = subst
  36 sub ident subst (App e1 e2) = App (sub ident subst e1) (sub ident subst e2)
  37 sub ident subst (Lambda v b)
  38         | ident <> v = Lambda v (sub ident b subst)
  39 sub _ _ x = x
  40
  41 eval :: Expression -> Eval Value
  42 eval (Let ident body rest) = eval body >>= \v->modify (\vs->[(ident, v):vs]) >>| eval rest
  43 eval (Lit v) = pure v
  44 eval (Var v) = gets (lookup v) >>= maybe (liftT (Left [toString v +++ " not found"])) pure
  45 eval (App e1 e2) = eval e1 >>= \(Func v)->v e2
  46 eval (Lambda a b) = pure (Func \arg->eval (sub a arg b))