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Added Non-Associative associativity for Pratt Parsers. #600
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YunkaiZhang233
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Original file line number | Diff line number | Diff line change |
---|---|---|
|
@@ -10,6 +10,8 @@ | |
//! ['binding power'](https://matklad.github.io/2020/04/13/simple-but-powerful-pratt-parsing.html#From-Precedence-to-Binding-Power) | ||
//! that determines how strongly operators should bind to the operands around them. | ||
//! | ||
//! Here is ['another approach'](https://www.engr.mun.ca/~theo/Misc/pratt_parsing.htm) that provides a more comprehensive perspective of handling multiple operators and patterns | ||
//! | ||
//! Pratt parsers are defined with the [`Parser::pratt`] method. | ||
//! | ||
//! When writing pratt parsers, it is necessary to first define an 'atomic' operand used by the parser for building up | ||
|
@@ -131,6 +133,8 @@ pub enum Associativity { | |
Left(u16), | ||
/// Specifies that the operator should be right-associative, with the given binding power (see [`right`]). | ||
Right(u16), | ||
/// Specifies that the operator should be non-associative, with the given binding power. | ||
Non(u16), | ||
} | ||
|
||
/// Specifies a left [`Associativity`] with the given binding power. | ||
|
@@ -149,18 +153,33 @@ pub fn right(binding_power: u16) -> Associativity { | |
Associativity::Right(binding_power) | ||
} | ||
|
||
/// Specifies a not-associative [`Associativity`] with the given binding power. | ||
/// | ||
/// Not-associative operators are evaluated from the left-most terms, moving rightward. | ||
pub fn non(binding_power: u16) -> Associativity {Associativity::Non(binding_power)} | ||
|
||
impl Associativity { | ||
fn left_power(&self) -> u32 { | ||
match self { | ||
Self::Left(x) => *x as u32 * 2, | ||
Self::Right(x) => *x as u32 * 2 + 1, | ||
Self::Left(x) => *x as u32 * 3, | ||
Self::Right(x) => *x as u32 * 3, | ||
Self::Non(x) => *x as u32 * 3, | ||
} | ||
} | ||
|
||
fn right_power(&self) -> u32 { | ||
match self { | ||
Self::Left(x) => *x as u32 * 2 + 1, | ||
Self::Right(x) => *x as u32 * 2, | ||
Self::Left(x) => *x as u32 * 3 + 1, | ||
Self::Right(x) => *x as u32 * 3, | ||
Self::Non(x) => *x as u32 * 3 + 1, | ||
} | ||
} | ||
|
||
fn next_power(&self) -> u32 { | ||
match self { | ||
Self::Left(x) => *x as u32 * 3, | ||
Self::Right(x) => *x as u32 * 3, | ||
Self::Non(x) => *x as u32 * 3 - 1, | ||
} | ||
} | ||
} | ||
|
@@ -467,7 +486,8 @@ macro_rules! impl_pratt_for_tuple { | |
// Infix binary operators | ||
$( | ||
let assoc = $X.associativity(); | ||
if $X::IS_INFIX && assoc.left_power() >= min_power { | ||
let mut upper_bound: u32 = u32::MAX; | ||
if $X::IS_INFIX && assoc.left_power() >= min_power && assoc.left_power() <= upper_bound { | ||
match $X.op_parser().go::<M>(inp) { | ||
Ok(op) => match recursive::recurse(|| self.pratt_go::<M, _, _, _>(inp, assoc.right_power())) { | ||
Ok(rhs) => { | ||
|
@@ -478,6 +498,7 @@ macro_rules! impl_pratt_for_tuple { | |
$X.fold_infix(lhs, op, rhs, &mut MapExtra::new(pre_expr.offset(), inp)) | ||
}, | ||
); | ||
upper_bound = assoc.next_power(); | ||
continue | ||
}, | ||
Err(()) => inp.rewind(pre_op), | ||
|
@@ -738,10 +759,9 @@ mod tests { | |
)) | ||
.map(|x| x.to_string()); | ||
|
||
assert_eq!( | ||
parser.parse("1+2!$*3").into_result(), | ||
Ok("(((1 + (2!))$) * 3)".to_string()), | ||
) | ||
assert!( | ||
parser.parse("§1+-~2!$*3").has_errors(), | ||
); | ||
Comment on lines
+762
to
+764
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. This change looks a little suspicious. Does this addition change the behaviour of existing parsers? |
||
} | ||
|
||
#[test] | ||
|
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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.There was a problem hiding this comment.
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Would this resolve the issue here?