JuliaLang/julia

ternary operator with "return" gives a parse error

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#9,180 opened on Nov 27, 2014

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Description

As discussed here: https://groups.google.com/forum/?fromgroups=#!topic/julia-users/9Ps2xYWSWMQ julia parses ternary operator with return not correct (or at least not intuitive).

function bar(x)
    x > 10 ? return(0) : nothing
    2
end

and

function bar(x)
    x > 10 ? return 0 : nothing
    2
end

result in "ERROR: syntax: colon expected in "?" expression".

The versions below work as expected.

function foo(x)
    x <= 10 ? nothing : return(0)
    2
end

or that

function foo(x)
    x > 10 ? (return 0) : nothing
    2
end

Contributor guide

Research direction
Examine the Julia parser's handling of the ternary operator with 'return'. Look at the parse code for '?' expressions, particularly how it handles 'return' as a statement within the expression. Trace the error path to understand why parentheses around 'return(0)' cause a parse error and why 'return' without parentheses fails.
Tech stack
julia
Domain
compilers
Issue type
Bug
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
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JuliaGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40