[Haskell-cafe] The 13-line example in Text.Megaparsec.Expr

26 Feb 2016

      At the bottom of the Hackage documentation for Text.Megaparsec.Expr [1] is
a 13-line demonstration program. It includes no import statements. I added
the ones I could deduce, which produced this:

    import Text.Megaparsec
    import Text.Megaparsec.Expr
    import Text.Megaparsec.Lexer (symbol,integer)

    parens = between (symbol "(") (symbol ")")

    expr = makeExprParser term table <?> "expression"

    term = parens expr <|> integer <?> "term"

    table = [ [ prefix  "-"  negate
              , prefix  "+"  id ]
            , [ postfix "++" (+1) ]
            , [ binary  "*"  (*)
              , binary  "/"  div  ]
            , [ binary  "+"  (+)
              , binary  "-"  (-)  ] ]

    binary  name f = InfixL  (reservedOp name >> return f)
    prefix  name f = Prefix  (reservedOp name >> return f)
    postfix name f = Postfix (reservedOp name >> return f)

That still won't compile, because GHC does not know what reservedOp means.
Does reservedOp refer to something that no longer exists, or have I just
not found it?

[1]
https://hackage.haskell.org/package/megaparsec-4.4.0/docs/Text-Megaparsec-Ex...

-- 
Jeffrey Benjamin Brown

[Haskell-cafe] The 13-line example in Text.Megaparsec.Expr

Jeffrey Brown