Have you ever been frustrated by having to add extra type information when using coerce or unsafeCoerce? Have you ever wanted to simply tell the compiler, ‘Just turn the Foos into Bars,’ without having to resort to coerce @([(a, Foo)] -> f b) @([(a, Bar)] -> f b) or coerceFooBar :: ([(a, Foo)] -> f b) -> [(a, Bar)] -> f b or similar to avoid complaints about how a can’t possibly be unified with a0?
If so, my new library coerce-with-substitution is for you.
With only two lines of value-level code[1], and no dependencies other than base, it is one of the lightest dependencies you could ever imagine adding to your project. It is also, I hope, one of the best documented. Even the unpublished source comments should be an informative and perhaps mildly entertaining read.
This is a candidate release; I’m very interested in the sort of feedback that would be difficult to incorporate after a formal release. Is something named poorly? Does some behavior surprise you? Is the documentation too verbose, missing any important details, or insufficiently Diátactic? I will probably hold off on making a permanent release until late July, so please let me know what you think I should change to make this the little library you’d want to use!
They are
coerceSubst = coerceandunsafeCoerceSubst = unsafeCoerce, and of course they’re markedINLINE. ↩︎