module Check.AST.Pattern.ConstFunc where

import Curry.SpanInfo
import Curry.Span
import Curry.Position
import Curry.Types
import Curry.Ident
import Text.Pretty

import Types

import Control.Applicative ( when )

-- Checks if the lambda function `\x y -> x` occurs in the code.
-- If so, a warning is emitted to use `const` instead.
checkConstFunc :: Expression a -> Int -> CSM ()
checkConstFunc e _ =
  case e of
    (Lambda
      sI
      [ (VariablePattern _ _ ident1)
      , (VariablePattern _ _ ident2)]
      (Variable _ _ (QualIdent _ _ ident3))) -> do when (ident1 == ident3)
                                                     (report ( Message
                                                               (getSpan sI)
                                                               ( text "superfluous code"
                                                               <+> colorizeKey "\\x y -> x"
                                                               )
                                                               ( text "instead of"
                                                               <+> colorizeKey "\\x y -> x"
                                                               <+> text "write"
                                                               <+> colorizeKey "const"
                                                               )
                                                             )
                                                     )
                                                   when (ident3 == ident2)
                                                     (report ( Message
                                                               (getSpan sI)
                                                               ( text "superfluous code"
                                                               <+> colorizeKey "\\x y -> y"
                                                               )
                                                               ( text "instead of"
                                                               <+> colorizeKey "\\x y -> y"
                                                               <+> text "write"
                                                               <+> colorizeKey "const"
                                                               <+> text "and switch parameters"
                                                               )
                                                             )
                                                     )
    _                                       -> return ()