Generated contracts for polymorphic vector types need to use impersonator contracts, not chaperone contracts
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- Dominant language
- Racket
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Description
This program fails with a contract error:
#lang typed/racket
(require/typed
racket/base
[vector-ref (All [a] (Vectorof a) Integer -> a)])
(vector-ref (vector 1 2 3) 1)
vector-ref: non-chaperone result;
received a result that is not a chaperone of the original result
original: 2
received: #<a4>
I think the generated contract that wraps the vector value needs to be an impersonator contract, not a chaperone contract.
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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 reproducing the typed/racket example from the issue and trace how the generated contract for (Vectorof a) is chosen for vector-ref. Compare the chaperone and impersonator behavior involved in the contract error. Done means the example evaluates without the reported non-chaperone result error.
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