Suggested type signature causes a type error (even though it appears correct)
The attached file, MWE.hs, contains an experiment attempting a rudimentary encoding of extensible ASTs in Haskell (without using compdata or a similar package relying upon OverlappingInstances and so forth). The definition of the upcast function appears to be correct. Compiling without a type signature produces a warning and the suggestion to include a type signature. Including the suggested type signature (which appears to be the correct one) causes a type error.
Trac metadata
Trac field | Value |
---|---|
Version | 7.4.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
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Blocking | |
CC | zep_haskell_trac@bahj.com |
Operating system | |
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