[Haskell-cafe] ANN: th-desugar simplifies Template Haskell processing

Richard Eisenberg eir at cis.upenn.edu
Mon Sep 2 03:25:35 CEST 2013

No, but I agree that this behavior is useful and in the spirit of th-desugar. I can add this to the next version, which should come out in a few days (tomorrow?), because I've noticed a bug with the scoping of as-patterns in let statements.

Thanks for the suggestion!

On Aug 31, 2013, at 12:06 PM, Sjoerd Visscher wrote:

> Great package!
> One question: Do you remove/inline type synonyms? I ask because I just ran into this with some TH code. I'm looking for types that end with -> a, but that fails when type synonyms are involved.
> Sjoerd
> On Aug 30, 2013, at 2:08 AM, Richard Eisenberg <eir at cis.upenn.edu> wrote:
>> I've just uploaded my new th-desugar package, which enables easier processing of Template Haskell source syntax by desugaring it into a much simpler core language. The meaning of the code after desugaring is identical to before desugaring, but the syntax is much simpler. To wit, th-desugar simplifies out all of the following constructs:
>> - guarded expressions in both functions and case statements
>> - "where" declarations
>> - do syntax
>> - list/monad comprehensions
>> - record creation / updates
>> - as patterns
>> - non-trivial patterns in a lambda expression
>> - lambda-case
>> - multi-way if
>> - several more
>> If you are writing a library that manipulates Template Haskell syntax, you may wish to consider if th-desugar will make your job easier by forcing you to consider fewer cases. The one source Haskell construct supported by Template Haskell but not supported by th-desguar is view patterns, mostly because these interact quite non-trivially with pattern binders. It's possible this hole will be closed in a future version.
>> Enjoy!
>> Richard
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