dkanus
588790b9b4
Huge dump of refactored code. Still in the middle of the changes that are to be squashed later in a one huge monster commit, because there is no value in anything atomic here.
94 lines
3.2 KiB
Rust
94 lines
3.2 KiB
Rust
//! Precedence tables for Fermented `UnrealScript` operators.
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//!
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//! These values don't follow the usual *binding power* convention for
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//! a Pratt parser, where tighter binding corresponds to a larger number.\
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//! Here, the smaller the number, the tighter the binding power.\
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//! For this reason, we use the term *precedence rank* instead.
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//!
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//! ## Operators sorted by precedence (lowest number = tighter binding)
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//!
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//! ### Infix operators
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//!
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//! All infix operators in `UnrealScript` are
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//! [left-associative](https://wiki.beyondunreal.com/Operators).
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//!
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//! 12: `**`
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//! 16: `*`, `/`, `Cross`, `Dot`
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//! 18: `%`
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//! 20: `+`, `-`
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//! 22: `<<`, `>>`, `>>>`
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//! 24: `<`, `>`, `<=`, `>=`, `==`, `~=`, `ClockwiseFrom`
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//! 26: `!=`
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//! 28: `&`, `^`, `|`
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//! 30: `&&`, `^^`
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//! 32: `||`
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//! 34: `*=`, `/=`, `+=`, `-=`
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//! 40: `$`, `*`, `@`
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//! 44: `$=`, `*=`, `@=`
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//! 45: `-=`
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//!
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//! Some operator, such as `*`, appear twice with different precedence
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//! ranks because they were defined with different values for different types
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//! in separate script source files (as in the Killing Floor sources).\
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//! However, `UnrealScript` uses only the first definition it encounters in
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//! `Object.uc`, which corresponds to the lower value.
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//!
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//! ### Prefix operators
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//!
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//! `!`, `~`, `+`, `-`, `++`, `--`.
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//!
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//! ### Postfix operators
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//!
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//! `++`, `--`.
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use crate::ast::{InfixOperator, infix_operator_info};
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use crate::lexer::Token;
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/// Compact precedence rank used by the Pratt Parser.
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///
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/// A smaller number means tighter binding, and a larger number means looser
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/// binding. This inverted scale matches how `UnrealScript` tables were recorded.
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#[must_use]
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#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
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pub struct PrecedenceRank(u8);
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impl PrecedenceRank {
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/// The loosest possible precedence rank.
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///
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/// In this inverted scale (smaller number = tighter binding),
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/// this is represented by the maximum [`u8`] value.
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pub const LOOSEST: Self = Self(u8::MAX);
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/// The tightest possible precedence rank.
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///
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/// In this inverted scale (smaller number = tighter binding),
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/// this is represented by zero.
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pub const TIGHTEST: Self = Self(0);
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/// Returns `true` if `self` has a looser binding than `other`.
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pub const fn is_looser_than(self, other: Self) -> bool {
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self.0 > other.0
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}
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}
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/// Maps a token to its infix operator along with its left and right binding
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/// ranks: `(left_precedence_rank, operator, right_precedence_rank)`.
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///
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/// Returns [`None`] if and only if `token` is not an infix operator.
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pub fn infix_precedence_ranks(
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token: Token,
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) -> Option<(PrecedenceRank, InfixOperator, PrecedenceRank)> {
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let info = infix_operator_info(token)?;
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// All operators are left-associative, so `right_precedence_rank` is set to
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// `left_binding_rank - 1` (with our "smaller is tighter" scale, this
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// enforces left associativity in Pratt parsing).
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//
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// Since all precedences are even, subtracting one won't actually cross
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// any boundary between operator groups.
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Some((
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PrecedenceRank(info.right_precedence_rank),
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info.operator,
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PrecedenceRank(info.right_precedence_rank - 1),
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))
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}
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