[Haskell-cafe] integrating Happy & Alex monads

Jason Dagit dagitj at gmail.com
Fri Dec 27 06:05:12 UTC 2013

I made this example specifically to help people with this problem (the
problem being that the documentation is spotty here).

It's the expression parser from the happy documentation using the monad
that alex can generate for you. It's the cleanest and simplest way (and
simplest example) that I found to merge the two. I should really submit
this as a documentation fix to happy.



On Thu, Dec 26, 2013 at 12:08 PM, Richard Cobbe <cobbe at ccs.neu.edu> wrote:

> I'm working on a program in which I'd like to use Alex and Happy to parse
> the input.  I've written the scanner, and it uses Alex's "monadUserState"
> wrapper to track source location and various other things.  Now, the
> problem is to integrate it with the parser.  As far as I can tell from
> reading the Happy documentation, I need to use a monadic Parser in Happy as
> well, but the manuals don't relaly provide a lot of information about how
> to integrate the two.  And I haven't really been able to find many examples
> of this either.  Lots of folks cite "the Haskell parser", although I'm not
> sure which implementation that's referring to.  I did check out the GHC
> source, and while it contains an Alex parser specification, it doesn't look
> like anything actually *uses* this, preferring instead a handwritten
> parser.
> Could anyone point me to a discussion of how to integrate these two tools,
> or examples of places where folks have done this before?
> Thanks much,
> Richard
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