構文解析は，式の解析から始める．
準備としてまず AST を定義する．
Expression
まずは基底クラスから作る．
expression.hpp
#include <memory>
#include <utility>
#include "pos.hpp"
namespace expression {
class Expression {
public:
pos::Range pos;
virtual ~Expression();
virtual void debug_print(int depth = 0) const = 0;
};
}
expression.cpp
#include "expression.hpp"
namespace expression {
Expression::~Expression() = default;
}
debug_print() はデバッグ出力用．式はネストするので，デバッグ出力時は debug_print() が再帰的に呼ばれる感じになる．引数 depth はその再帰の深さで，出力をインデントするのに使う．イメージとしては，(1 + 2) * (3 - 4) が
Mul
Add
1
2
Sub
3
4
とか
1
Add
2
Mul
3
Sub
4
みたくなってほしい．
Identifier
単一の識別子は，式．
expression.hpp
#include <string>
namespace expression {
class Identifier : public Expression {
std::string name;
public:
Identifier(std::string);
void debug_print(int) const override;
};
}
expression.cpp
#include <iostream>
#include <string_view>
namespace expression {
Identifier::Identifier(std::string name): name(std::move(name)) {}
static constexpr std::string_view INDENT = " ";
void Identifier::debug_print(int depth) const {
for(int i = 0; i < depth; ++i) std::cout << INDENT;
std::cout << pos << ": Identifier(" << name << ")" << std::endl;
}
}
Integer
単一の整数リテラルも，式．
expression.hpp
#include <cstddef>
namespace expression {
class Integer : public Expression {
std::int32_t value;
public:
Integer(std::int32_t);
void debug_print(int) const override;
};
}
expression.cpp
namespace expression {
Integer::Integer(std::int32_t value): value(value) {}
void Integer::debug_print(int depth) const {
for(int i = 0; i < depth; ++i) std::cout << INDENT;
std::cout << pos << ": Integer(" << value << ")" << std::endl;
}
}
Unary
式の前に単項演算子が付いたものも式．
まずは演算子を表す enum class を定義して，
expression.hpp
namespace expression {
enum class UnaryOperator {
Plus, Minus,
LogicalNot, BitNot
};
}
演算子と式の組として定義する．
expression.hpp
namespace expression {
class Unary : public Expression {
UnaryOperator unary_operator;
std::unique_ptr<Expression> operand;
public:
Unary(UnaryOperator, std::unique_ptr<Expression>);
void debug_print(int) const override;
};
}
expression.cpp
namespace expression {
Unary::Unary(
UnaryOperator unary_operator,
std::unique_ptr<Expression> operand
):
unary_operator(unary_operator),
operand(std::move(operand)) {}
void Unary::debug_print(int depth) const {
std::string_view name;
switch(unary_operator){
case UnaryOperator::Plus: name = "plus"; break;
case UnaryOperator::Minus: name = "minus"; break;
case UnaryOperator::LogicalNot: name = "logical not"; break;
case UnaryOperator::BitNot: name = "bitwise not";
}
for(int i = 0; i < depth; ++i) std::cout << INDENT;
std::cout << pos << ": Unary(" << name << ")" << std::endl;
operand->debug_print(depth + 1);
}
}
debug_print() の実装は以後省略．
Binary
二項演算子も同様に定義する．
expression.hpp
namespace expression {
enum class BinaryOperator {
Mul, Div, Rem,
Add, Sub,
LeftShift, RightShift,
BitAnd, BitOr, BitXor,
Equal, NotEqual,
Less, Greater,
LessEqual, GreaterEqual,
LogicalAnd, LogicalOr,
Assign,
MulAssign, DivAssign, RemAssign, AddAssign, SubAssign,
BitAndAssign, BitOrAssign, BitXorAssign,
RightShiftAssign, LeftShiftAssign
};
class Binary : public Expression {
BinaryOperator binary_operator;
std::unique_ptr<Expression> left, right;
public:
Binary(BinaryOperator, std::unique_ptr<Expression>, std::unique_ptr<Expression>);
void debug_print(int) const override;
};
}
expression.cpp
namespace expression {
Binary::Binary(
BinaryOperator binary_operator,
std::unique_ptr<Expression> left,
std::unique_ptr<Expression> right
):
binary_operator(binary_operator),
left(std::move(left)),
right(std::move(right)) {}
}
Invocation
関数の呼び出しは，呼び出される関数と，引数の std::vector の組として表す．
expression.hpp
namespace expression {
class Invocation : public Expression {
std::unique_ptr<Expression> function;
std::vector<std::unique_ptr<Expression>> arguments;
public:
Invocation(std::unique_ptr<Expression>, std::vector<std::unique_ptr<Expression>>);
void debug_print(int) const override;
};
}
expression.cpp
namespace expression {
Invocation::Invocation(
std::unique_ptr<Expression> function,
std::vector<std::unique_ptr<Expression>> arguments
):
function(std::move(function)),
arguments(std::move(arguments)) {}
}