I'm trying this again! The comment for Megaparsec.makeExprParser refers to "parens". When I grep for "parens" in Megaparsec I get only two occurences, both of them in comments:

    ./Lexer.hs:-- > parens    = between (symbol "(") (symbol ")")

    ./Expr.hs:-- > term = parens expr <|> integer <?> "term"

If I try defining parens as in the comment from Lexer.hs, I get these errors:

    <interactive>:37:33:

        Couldn't match type ‘Char’ with ‘()’

        Expected type: [()]

          Actual type: [Char]

        In the first argument of ‘symbol’, namely ‘"("’

        In the first argument of ‘between’, namely ‘(symbol "(")’

        In the expression: between (symbol "(") (symbol ")")

    

    <interactive>:37:46:

        Couldn't match type ‘Char’ with ‘()’

        Expected type: [()]

          Actual type: [Char]

        In the first argument of ‘symbol’, namely ‘")"’

        In the second argument of ‘between’, namely ‘(symbol ")")’

        In the expression: between (symbol "(") (symbol ")")

[1] https://hackage.haskell.org/package/megaparsec-5.0.1/docs/Text-Megaparsec-Expr.html

On Mon, Feb 29, 2016 at 2:05 AM, Özgür Akgün <ozgurakgun@gmail.com> wrote:

On 29 February 2016 at 08:22, Stephen Tetley <stephen.tetley@gmail.com> wrote:

For the expression parser, Megaparsec's documentation is wrong[*] and
probably it should use symbol rather than reservedOp. Note that symbol
is slightly different in Megaparsec as it's a plain combinator (rather
than one instantiated from a first class module as in Parsec) so it
takes two args rather than one.


[*] Well, likely wrong - I haven't got round to using Megaparsec yet.

You are right: https://github.com/mrkkrp/megaparsec/commit/750adb7c70392c3195eda12d816f4a1a2305321e

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Özgür Akgün

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