[RFC]: add support for eager evaluation of side-effect free code in the REPL #2073
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difficulty: 4
Likely to be moderately difficult.
Enhancement
Issue or pull request for enhancing existing functionality.
JavaScript
Issue involves or relates to JavaScript.
Needs Discussion
Needs further discussion.
priority: Normal
Normal priority concern or feature request.
REPL
Issue or pull request specific to the project REPL.
RFC
Request for comments. Feature requests and proposed changes.
Description
This RFC proposes adding support for eager evaluation of side-effect free code in the REPL. E.g.,
would trigger a preview below the input command, where
<|>
represents the cursor. Upon hitting ENTER, the command would execute with the result displayed after the output prompt, as normal.This feature is now implemented in browser devtools, such as Chrome (see https://developer.chrome.com/blog/new-in-devtools-68/#eagerevaluation).
The tricky bit with implementing this is detecting side effects. And we'd likely want to avoid eagerly evaluating things like HTTP requests. Additionally, we'd like want to exclude things which are not idempotent (e.g., PRNGs,
Date
constructor, etc).There is also the concern as to how to handle eager evaluation of computationally expensive commands or commands returning large outputs.
As this feature may not be desired by all users, we should presumably support an option for enabling/disabling this on REPL instantiation. And we should disable eager evaluation when not in TTY mode.
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