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

Sjoerd Visscher sjoerd at w3future.com
Sat Aug 31 18:06:37 CEST 2013

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.


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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