gleam-lang/gleam

Avoid calling `bitArraySliceToFloat` in generated JS for float patterns

Open

#4658 opened on Jun 2, 2025

View on GitHub
 (2 comments) (0 reactions) (0 assignees)Rust (21,417 stars) (960 forks)batch import
help wanted

Description

Today when using a :float bit array pattern the bitArraySliceToFloat function is called twice with the same arguments. This is wasted work!

Change the code generator to do it only once, saving the result to a variable to use twice.

Contributor guide

Tech stack
rustjavascript
Domain
backendtooling
Issue type
performance
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.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Gleam compiler JS codegenJavaScriptCode generation
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Examine the JavaScript code generator in the Gleam compiler (likely in `src/codegen/js.rs` or `src/backends/js.rs`) to locate where `bitArraySliceToFloat` is invoked for float patterns. Identify the duplication and refactor to introduce a temporary variable to store the result. Test that the generated JavaScript still produces correct output.