Base.hs

module Calculator.Evaluator.Base (evaluate) where

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import Calculator.Prim.Expr (Bindings, Expr(..))
import Calculator.Parser.Statement (parseStat)
import Calculator.Evaluator.Statement (evalStat)

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import Text.ParserCombinators.Parsec (parse, eof)
import Control.Applicative ((<*))

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eval :: Bindings -> String -> Either Expr Bindings
eval b inp = case parse (parseStat <* eof) "Statement" inp of
              Left e  -> Left $ InvalidError $ show e
              Right s -> evalStat b s

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result :: Either Expr Bindings -> Either String Bindings
result e = case e of
            Left (Constant c)     -> Left $ show c
            Left (InvalidError x) -> Left x
            Right b               -> Right b

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evaluate :: Bindings -> String -> Either String Bindings
evaluate b s = result $ eval b s

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