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108 lines
3.6 KiB
C++
108 lines
3.6 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef CARBON_TOOLCHAIN_PARSE_PRECEDENCE_H_
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#define CARBON_TOOLCHAIN_PARSE_PRECEDENCE_H_
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#include <optional>
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#include "toolchain/lex/token_kind.h"
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namespace Carbon::Parse {
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// Given two operators `$` and `@`, and an expression `a $ b @ c`, how should
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// the expression be parsed?
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enum class OperatorPriority : int8_t {
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// The left operator has higher precedence: `(a $ b) @ c`.
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LeftFirst = -1,
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// The expression is ambiguous.
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Ambiguous = 0,
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// The right operator has higher precedence: `a $ (b @ c)`.
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RightFirst = 1,
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};
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enum class Associativity : int8_t {
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LeftToRight = -1,
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None = 0,
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RightToLeft = 1
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};
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// A precedence group associated with an operator or expression.
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class PrecedenceGroup {
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public:
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struct Trailing;
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// Objects of this type should only be constructed using the static factory
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// functions below.
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PrecedenceGroup() = delete;
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// Get the sentinel precedence level for a postfix expression. All operators
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// have lower precedence than this.
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static auto ForPostfixExpr() -> PrecedenceGroup;
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// Get the precedence level for a top-level or parenthesized expression. All
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// expression operators have higher precedence than this.
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static auto ForTopLevelExpr() -> PrecedenceGroup;
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// Get the sentinel precedence level for a statement context. All operators,
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// including statement operators like `=` and `++`, have higher precedence
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// than this.
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static auto ForExprStatement() -> PrecedenceGroup;
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// Get the precedence level at which to parse a type expression. All type
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// operators have higher precedence than this.
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static auto ForType() -> PrecedenceGroup;
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// Get the precedence level at which to parse the type expression between
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// `impl` and `as`.
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static auto ForImplAs() -> PrecedenceGroup;
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// Look up the operator information of the given prefix operator token, or
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// return std::nullopt if the given token is not a prefix operator.
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static auto ForLeading(Lex::TokenKind kind) -> std::optional<PrecedenceGroup>;
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// Look up the operator information of the given infix or postfix operator
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// token, or return std::nullopt if the given token is not an infix or postfix
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// operator. `infix` indicates whether this is a valid infix operator, but is
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// only considered if the same operator symbol is available as both infix and
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// postfix.
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static auto ForTrailing(Lex::TokenKind kind, bool infix)
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-> std::optional<Trailing>;
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friend auto operator==(PrecedenceGroup lhs, PrecedenceGroup rhs) -> bool {
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return lhs.level_ == rhs.level_;
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}
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// Compare the precedence levels for two adjacent operators.
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static auto GetPriority(PrecedenceGroup left, PrecedenceGroup right)
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-> OperatorPriority;
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// Get the associativity of this precedence group.
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auto GetAssociativity() const -> Associativity {
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return static_cast<Associativity>(GetPriority(*this, *this));
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}
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private:
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// We rely on implicit conversions via `int8_t` for enumerators defined in the
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// implementation.
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// NOLINTNEXTLINE(google-explicit-constructor)
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PrecedenceGroup(int8_t level) : level_(level) {}
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// The precedence level.
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int8_t level_;
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};
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// Precedence information for a trailing operator.
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struct PrecedenceGroup::Trailing {
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// The precedence level.
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PrecedenceGroup level;
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// `true` if this is an infix binary operator, `false` if this is a postfix
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// unary operator.
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bool is_binary;
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};
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} // namespace Carbon::Parse
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#endif // CARBON_TOOLCHAIN_PARSE_PRECEDENCE_H_
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