CakeML/cakeml

Add contains to Char module

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#1,433 opened on Jul 18, 2026

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 (0 comments) (0 reactions) (0 assignees)Standard ML (98 forks)auto 404
basis extensionsgood first issuelow effort

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Description

It would be useful to have Char.contains in part of the basis. One simple implementation is the following:

fun contains s c = List.member c (String.explode s)

However, I would suspect that it would be better to avoid the explode and iterate over the string instead for the definition that ends up being translated. It might be neat to prove a theorem of equivalence between them, though.

Contributor guide

Research direction
Study the existing Char module to understand the pattern for adding functions, then implement Char.contains by iterating over the string (avoiding explode). Optionally, prove an equivalence theorem between the simple list based implementation and the iterating version.
Tech stack
None
Domain
compilers
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Standard MLGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60