Skip to content

starlark: Support chaining expressions #35

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
robinlinden merged 2 commits into from
Mar 8, 2026
Merged

starlark: Support chaining expressions #35

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
bea3951
starlark: Make expression-parsing nicer
robinlinden Mar 6, 2026
b8e2cf2
starlark: Support chaining expressions
robinlinden Mar 6, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
98 changes: 56 additions & 42 deletions starlark/parser.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -272,63 +272,77 @@ class Parser {
}

std::optional<Expression> parse_expression(Token &token) {
auto operand = parse_operand(token);
if (!operand) {
auto expr = parse_operand(token);
if (!expr) {
std::cerr << "Failed to parse operand.\n";
return std::nullopt;
}

auto next = next_token();
if (!next) {
// This is fine.
} else if (std::holds_alternative<token::LParen>(*next)) {
auto args = parse_argument_list();
if (!args) {
std::cerr << "Failed to parse argument list.\n";
return std::nullopt;
}

return CallExpr{
.target = std::make_shared<Expression>(std::move(*operand)),
.args = std::move(*args),
};
} else if (std::holds_alternative<token::LBracket>(*next)) {
next = next_token();
while (true) {
auto next = next_token();
if (!next) {
std::cerr << "Unexpected end of input after '['.\n";
return std::nullopt;
return expr;
}

auto index_expr = parse_expression(*next);
if (!index_expr) {
std::cerr << "Failed to parse index expression.\n";
return std::nullopt;
if (std::holds_alternative<token::LParen>(*next)) {
auto args = parse_argument_list();
if (!args) {
std::cerr << "Failed to parse argument list.\n";
return std::nullopt;
}

expr = CallExpr{
.target = std::make_shared<Expression>(std::move(*expr)),
.args = std::move(*args),
};

continue;
}

if (!expect_next_token(token::RBracket{})) {
return std::nullopt;
if (std::holds_alternative<token::LBracket>(*next)) {
next = next_token();
if (!next) {
std::cerr << "Unexpected end of input after '['.\n";
return std::nullopt;
}

auto index_expr = parse_expression(*next);
if (!index_expr) {
std::cerr << "Failed to parse index expression.\n";
return std::nullopt;
}

if (!expect_next_token(token::RBracket{})) {
return std::nullopt;
}

expr = SliceExpr{
.target = std::make_shared<Expression>(std::move(*expr)),
.index = std::make_shared<Expression>(std::move(*index_expr)),
};

continue;
}

return SliceExpr{
.target = std::make_shared<Expression>(std::move(*operand)),
.index = std::make_shared<Expression>(std::move(*index_expr)),
};
} else if (std::holds_alternative<token::Dot>(*next)) {
auto member_token = next_token();
if (!member_token || !std::holds_alternative<token::Identifier>(*member_token)) {
std::cerr << "Expected identifier after '.'.\n";
return std::nullopt;
if (std::holds_alternative<token::Dot>(*next)) {
auto member_token = next_token();
if (!member_token || !std::holds_alternative<token::Identifier>(*member_token)) {
std::cerr << "Expected identifier after '.'.\n";
return std::nullopt;
}

expr = MemberExpr{
.target = std::make_shared<Expression>(std::move(*expr)),
.member = Identifier{.name = std::get<token::Identifier>(*member_token).name},
};

continue;
}

return MemberExpr{
.target = std::make_shared<Expression>(std::move(*operand)),
.member = Identifier{.name = std::get<token::Identifier>(*member_token).name},
};
} else {
// We didn't end up using the next token, so put it back for later.
reconsume(std::move(*next));
return expr;
}

return operand;
}

std::optional<std::vector<Argument>> parse_argument_list() {
Expand Down
33 changes: 33 additions & 0 deletions starlark/parser_test.cc
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -292,6 +292,39 @@ int main() {
},
},
},
{
"foo.baz[3].qux().bar",
starlark::Program{
.statements{
starlark::ExpressionStmt{
.expr{
starlark::MemberExpr{
.target = std::make_shared<starlark::Expression>(starlark::CallExpr{
.target =
std::make_shared<starlark::Expression>(starlark::MemberExpr{
.target = std::make_shared<
starlark::Expression>(starlark::SliceExpr{
.target = std::make_shared<starlark::Expression>(
starlark::MemberExpr{
.target =
std::make_shared<starlark::Expression>(
starlark::Identifier{"foo"}),
.member = starlark::Identifier{"baz"},
}),
.index = std::make_shared<starlark::Expression>(
starlark::IntLiteral{3}),
}),
.member = starlark::Identifier{"qux"},
}),
.args{},
}),
.member = starlark::Identifier{"bar"},
},
},
},
},
},
},
});

// TODO(robinlinden): Return error codes from parser and use that here.
Expand Down