10000 Multiple variable pattern support · Issue #1061 · lalrpop/lalrpop · GitHub
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Multiple variable pattern support #1061

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A4-Tacks opened this issue May 4, 2025 · 3 comments
Open

Multiple variable pattern support #1061

A4-Tacks opened this issue May 4, 2025 · 3 comments

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@A4-Tacks
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A4-Tacks commented May 4, 2025 
grammar;

Or<A, B> = { A B, B A }
pub Foo: String = <x:Or<"a", "b">> => {
    let (a, b) = x;
    a.to_string() + b
};

Rewritten to:

grammar;

Or<A, B> = { A B, B A }
pub Foo: String = <(a, b):Or<"a", "b">> => {
    a.to_string() + b
};

And support such as <(mut a, b):Bar>, <(a, (b, c)):Baz>
@chanbengz
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LALRPOP supports a shorthand <>. See https://lalrpop.github.io/lalrpop/tutorial/003_type_inference.html.

I would suggest using that

grammar;

Or<A, B> = { A B, B A }
pub Foo: String = Or<"a", "b"> => {
    format!("{}{}", <>.0, <>.1)
};

And support such as <(mut a, b):Bar>, <(a, (b, c)):Baz>

I see your point, but IMO this is weird because <> simply solves the problem. The only problem is that it might not be so "readable".

@A4-Tacks
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A4-Tacks commented May 4, 2025

When containing deep nesting, it is very difficult to read without using patterns to untangle it

@dburgener dburgener mentioned this issue May 9, 2025
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@dburgener
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I think that having support for this added syntax would be a value-add, although as @chanbengz points out, there are existing ways to express this situation pretty well.

I would say that I'm certainly open to accepting PRs that add this syntax if someone wants to submit one.

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@dburgener @chanbengz @A4-Tacks
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