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

I found the answer to my most recent question while reading this tutorial[1] on megaparsec. Thanks, and apologies for the noise. [1] https://mrkkrp.github.io/megaparsec/tutorials/parsing-simple-imperative-lang... On Sat, Sep 24, 2016 at 12:45 AM, Jeffrey Brown wrote:

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 wrote:

...

On 29 February 2016 at 08:22, Stephen Tetley 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/750adb7c7 0392c3195eda12d816f4a1a2305321e

-- Özgür Akgün

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-- Jeff Brown | Jeffrey Benjamin Brown Website https://msu.edu/~brown202/ Facebook https://www.facebook.com/mejeff.younotjeff LinkedIn https://www.linkedin.com/in/jeffreybenjaminbrown (InMail is unreliable) Github https://github.com/jeffreybenjaminbrown