JuliaLang/julia

Improve documentation for `esc`

Open

#37,122 opened on Aug 19, 2020

View on GitHub
 (4 comments) (0 reactions) (0 assignees)Julia (5,773 forks)batch import
docsgood first issue

Repository metrics

Stars
 (48,709 stars)
PR merge metrics
 (Avg merge 20d 6h) (157 merged PRs in 30d)

Description

esc(e)

  Only valid in the context of an Expr returned from a macro. Prevents the macro hygiene pass from turning embedded variables into gensym variables. See the Macros section of the Metaprogramming chapter of the manual for more details and examples.

I'm not sure what "valid" really means here, since

julia> esc(:(x, ))
:($(Expr(:escape, :((x,)))))

It could mean "you can't eval the resulting expression":

julia> eval(esc(:(x, )))
ERROR: syntax: invalid syntax (escape (call (core tuple) (outerref x)))

Contributor guide

Research direction
Read the existing documentation for `esc`, understand its usage in macros, and write a clearer explanation that addresses the confusion about what 'valid' means.
Tech stack
None
Domain
backend
Issue type
Documentation
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
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
Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80