EvTerms and how they are used

Jan Bracker jan.bracker at googlemail.com
Wed Feb 25 10:55:43 UTC 2015


I am trying to use the new type checker plugins [1] that are implemented in

When successful a plugin has to return a [(EvTerm, Ct)] for the solved
constraints. The documentation on EvTerms is scarce [2,3,4] and I could not
find papers that explain them (many talk about 'evidence', but they never
get concrete).

So far I have figured out that "EvDFunApp DFunId [Type] [EvTerm]" selects a
certain instance to be used for a constraint, though I don't know what the
list of EvTerms in the end is for. I am also a bit unclear on how the
"[Type]" is used.If I turn on '-dcore-lint' I get errors. So I still seem
to be using it wrong.

I have also asked in IRC, but did not get a response to my question.

I am sorry if this is the wrong mailing list to ask. If there is a more
apropriate place just point it out.


[1]: https://ghc.haskell.org/trac/ghc/wiki/Plugins/TypeChecker
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