module Calculator.Evaluator.Cmd (evalCmd) where

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import           Calculator.Evaluator.Expr   (evalExpr)
import           Calculator.Evaluator.Func   (execFunc)
import           Calculator.Help             (help)
import           Calculator.Prim.Bindings    (Bindings, addFun, addVar, display)
import           Calculator.Prim.Cmd         (Cmd (..))
import           Calculator.Prim.Definitions (defBinds)
import           Calculator.Prim.Expr        (Expr (Message, Constant))
import           Calculator.Prim.Function    (testFunc)

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evalCmd :: Bindings -> Cmd -> Either [String] Bindings
evalCmd _ Help    = Left help
evalCmd b Display = Left $ display b
evalCmd _ Reset   = Right defBinds
evalCmd b (Assign s e)   =
    case evalExpr b e of
      Message xxs -> Left xxs
      Constant c  -> Right $ addVar (s, c) b
      _           -> Left [" ~~ Erroneous Result ~~ "]
evalCmd b fun@(Func i _ _) = let f = execFunc b fun
                             in case testFunc f 0 of
                                  Nothing -> Right $ addFun (i, f) b
                                  Just ms -> Left ms

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