racket/typed-racket

case-lambda allows multiple cases with the same arity

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#517 opened on Mar 24, 2017

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Description

[I originally opened this as an issue for racket, but it more clearly violates the docs for typed/racket.]

Although for racket it doesn't seem explicitly forbidden, the typed/racket docs say:

Note that each formals must have a different arity.

Should this perhaps be an expansion-time error:

> (case-lambda [([z : Zero]) z]
               [([o : One]) o])
- : (-> Zero Zero)

This came up because a student encountering the case-> type constructor wondered whether case-lambda would provide overloading by type.

Contributor guide

Research direction
Add an expansion time check to ensure that each formals in case lambda have a different arity, and emit an error if not.
Tech stack
None
Domain
compilerstooling
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Racket
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75