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https://github.com/carbon-language/carbon-lang.git
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Geoff RomerandJon Meow
6ac3adfa53
`Pattern` is intended to pilot some changes I would like to apply to all our sum types: - The alternatives are expressed as derived classes rather than members of a `std::variant`. - The alternatives are classes in the [style guide sense](https://google.github.io/styleguide/cppguide.html#Structs_vs._Classes), meaning they can have invariants, but can't have public data members. - Creating an object is expressed using a constructor rather than a factory function. - Accessing an alternative is expressed as a cast (using LLVM's RTTI system) rather than `std::get` or a `Get` method. Co-authored-by: Jon Meow <46229924+jonmeow@users.noreply.github.com>
107 lines
3.4 KiB
C++
107 lines
3.4 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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#include "executable_semantics/ast/pattern.h"
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#include <string>
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#include "common/ostream.h"
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#include "executable_semantics/ast/expression.h"
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#include "executable_semantics/common/error.h"
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#include "llvm/ADT/StringExtras.h"
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#include "llvm/Support/Casting.h"
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namespace Carbon {
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using llvm::cast;
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void Pattern::Print(llvm::raw_ostream& out) const {
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switch (Tag()) {
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case Kind::AutoPattern:
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out << "auto";
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break;
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case Kind::BindingPattern: {
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const auto& binding = cast<BindingPattern>(*this);
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if (binding.Name().has_value()) {
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out << *binding.Name();
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} else {
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out << "_";
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}
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out << ": " << *binding.Type();
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break;
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}
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case Kind::TuplePattern: {
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const auto& tuple = cast<TuplePattern>(*this);
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out << "(";
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llvm::ListSeparator sep;
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for (const TuplePattern::Field& field : tuple.Fields()) {
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out << sep << field.name << " = " << field.pattern;
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}
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out << ")";
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break;
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}
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case Kind::AlternativePattern: {
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const auto& alternative = cast<AlternativePattern>(*this);
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out << alternative.ChoiceType() << "." << alternative.AlternativeName()
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<< alternative.Arguments();
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break;
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}
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case Kind::ExpressionPattern:
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out << cast<ExpressionPattern>(*this).Expression();
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break;
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}
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}
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TuplePattern::TuplePattern(const Expression* tuple_literal)
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: Pattern(Kind::TuplePattern, tuple_literal->line_num) {
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const auto& tuple = tuple_literal->GetTupleLiteral();
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for (const FieldInitializer& init : tuple.fields) {
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fields.push_back(Field(init.name, new ExpressionPattern(init.expression)));
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}
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}
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auto PatternFromParenContents(int line_num,
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const ParenContents<Pattern>& paren_contents)
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-> const Pattern* {
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std::optional<const Pattern*> single_term = paren_contents.SingleTerm();
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if (single_term.has_value()) {
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return *single_term;
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} else {
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return TuplePatternFromParenContents(line_num, paren_contents);
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}
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}
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auto TuplePatternFromParenContents(int line_num,
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const ParenContents<Pattern>& paren_contents)
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-> const TuplePattern* {
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return new TuplePattern(
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line_num, paren_contents.TupleElements<TuplePattern::Field>(line_num));
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}
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AlternativePattern::AlternativePattern(int line_num,
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const Expression* alternative,
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const TuplePattern* arguments)
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: Pattern(Kind::AlternativePattern, line_num), arguments(arguments) {
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if (alternative->tag() != ExpressionKind::FieldAccessExpression) {
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FATAL_USER_ERROR(alternative->line_num)
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<< "Alternative pattern must have the form of a field access.";
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}
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const auto& field_access = alternative->GetFieldAccessExpression();
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choice_type = field_access.aggregate;
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alternative_name = field_access.field;
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}
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auto ParenExpressionToParenPattern(const ParenContents<Expression>& contents)
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-> ParenContents<Pattern> {
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ParenContents<Pattern> result = {
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.elements = {}, .has_trailing_comma = contents.has_trailing_comma};
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for (const auto& element : contents.elements) {
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result.elements.push_back(
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{.name = element.name, .term = new ExpressionPattern(element.term)});
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}
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return result;
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}
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} // namespace Carbon
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