(U (List T) (List T T)) should be equivalent to (Pairof T (U Null (Pairof T Null)))
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- Racket
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Description
What version of Racket are you using?
6.6.0.5
What program did you run?
#lang typed/racket
(λ ([x : (U Null (Pairof Number (U Null (Pairof Number Null))))])
(ann x (U (List)
(List Number)
(List Number Number))))
What should have happened?
The program should typecheck successfully, as the two types are equivalent. With (U (List) (List Number)) TR recognizes the equivalence, but not with two or more elements.
If you got an error message, please include it here.
Type Checker: type mismatch
expected: (U Null (List Number) (List Number Number))
given: (U Null (Pairof Number (U Null (List Number)))) in: x
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the supplied typed/racket program with Racket 6.6.0.5 and examining the type-checker behavior for the two-element list union. Done means the program typechecks and the reported union of pairs is recognized as equivalent to the corresponding list union.
Written by the indexing model from the issue text.
Assessment
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100