Avoid copying elements when parsing #35
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MichaReiser commented May 15, 2023
Comment on lines 1613 to +1620
| OneOrMore<T>: Vec<T> = { | ||
| <i1: T> <i2:("," T)*> => { | ||
| let mut items = vec![i1]; | ||
| items.extend(i2.into_iter().map(|e| e.1)); | ||
| items | ||
| <e:T> => vec![e], | ||
| <mut v: OneOrMore<T>> "," <e:T> => { | ||
| v.push(e); | ||
| v | ||
| } | ||
| }; |
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This should be the same as
#[inline] OneOrMore<T>: Vec<T> = { <mut v: (<T> ",")*> <last:T> => { v.push(last); v } } But this doesn't work for reasons I do not understand. I don't know if both macros will expand to the same code or not.
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Though I am not a parser professional, it seems to related to lookahead.
It is using a sort of table lookup.
MichaReiser changed the title 
youknowone approved these changes May 15, 2023
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Great, the generated parser is also a lot smaller
Comment on lines 1613 to +1620
| OneOrMore<T>: Vec<T> = { | ||
| <i1: T> <i2:("," T)*> => { | ||
| let mut items = vec![i1]; | ||
| items.extend(i2.into_iter().map(|e| e.1)); | ||
| items | ||
| <e:T> => vec![e], | ||
| <mut v: OneOrMore<T>> "," <e:T> => { | ||
| v.push(e); | ||
| v | ||
| } | ||
| }; |
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Though I am not a parser professional, it seems to related to lookahead.
It is using a sort of table lookup.
| ) | ||
| }, | ||
| <location:@L> "match" <subject:TestOrStarNamedExpr> "," <subjects:OneOrMore<TestOrStarNamedExpr>> ","? ":" "\n" Indent <cases:MatchCase+> Dedent => { | ||
| <location:@L> "match" <subjects:TwoOrMore<TestOrStarNamedExpr, ",">> ","? ":" "\n" Indent <cases:MatchCase+> Dedent => { |
youknowone added a commit to youknowone/RustPython that referenced this pull request May 15, 2023
youknowone added a commit to RustPython/RustPython that referenced this pull request May 15, 2023
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This PR tries to reduce the number of elements that we copy by
vec.extendvec.insert(0, element)map|x| x.1)to ignore some tokens#Performance
I hoped that this would improve performance more but it remains mostly unchanged