Added Non-Associative associativity for Pratt Parsers. #600
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zesterer
reviewed
Feb 6, 2024
| match self { | ||
| Self::Left(x) => *x as u32 * 3, | ||
| Self::Right(x) => *x as u32 * 3, | ||
| Self::Non(x) => *x as u32 * 3 - 1, |
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For this to be valid, all powers should have 1 added to them such that *x as u32 * 3 - 1 can never result in underflow.
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Would this resolve the issue here?
Self::Left(x) => *x as u32 * 3 + 1,
Self::Right(x) => *x as u32 * 3 + 1,
Self::Non(x) => *x as u32 * 3 - 1,
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| assert!( | ||
| parser.parse("§1+-~2!$*3").has_errors(), | ||
| ); |
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This change looks a little suspicious. Does this addition change the behaviour of existing parsers?
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In current Pratt parsers, only associativity type of
leftandrightare supported. However, according to the original designs of Pratt parsing, it should also support Non-Associative infix binary operators.For example, consider operators
==as a non-associative operator. We should be able to identify it as non-associative and therefore rejecting1 == 2 == 3as an expression with the numbers being atomic literals. Whilst the current design only allow==to be either left-associative or right-associative.This PR added associativity
nonfor infix binary operators, and changed the binding power calculation function slightly based on The Original Parsing Methodology and this article.