JuliaLang/julia

Improve documentation for `esc`

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#37,122 opened on Aug 19, 2020

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docsgood first issue

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

Tech stack
None
Domain
documentation
Issue type
documentation
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.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
unclear
Prerequisites
understanding of Julia macrosfamiliarity with metaprogramming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Examine the current docstring of `esc` in the Julia source code (e.g., base/docs/helpdb/Base.jl or similar). Research the behavior of `esc` in various macro contexts to clarify what 'valid' means. Update the docstring to explicitly state that `esc` only works within a macro definition, not when called standalone, and provide examples of valid and invalid uses. Reference the Metaprogramming chapter for further details.