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implementation module Simple
import StdString
import WhileCommon
import Common
instance toString Stm
where
toString (Ass v a) = v <+ " := " <+ a
toString (If b s1 s2) = "if " <+ b <+ " then " <+ s1 <+ " else " <+ s2
toString (While b s) = "while " <+ b <+ " do " <+ s
toString Skip = "skip"
toString (Compose s1 s2) = s1 <+ "; " <+ s2
instance run Stm
where
run :: Stm State -> Either Error State
run (Ass v e) st // Assign e to v
= pure (\w -> if (w == v) (eval e st) (st w))
run (If b s1 s2) st // If b then s1 else s2
= eval b st >>= \r -> run (if r s1 s2) st
run w=:(While b s) st // While b do s
= eval b st >>= \r -> if r
(run s st >>= run w)
(pure st)
run Skip st // Skip
= pure st
run (Compose s1 s2) st // s1 ; s2
= run s1 st >>= run s2
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