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starlark: Support any expression as the lhs of a callexpr #30

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Merged
robinlinden merged 2 commits into from
Feb 27, 2026
Merged

starlark: Support any expression as the lhs of a callexpr #30

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761f07a
starlark: Split out operand-parsing from expression-parsing
robinlinden Feb 25, 2026
9618121
starlark: Support any expression as the lhs of a callexpr
robinlinden Feb 25, 2026
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8 changes: 6 additions & 2 deletions starlark/ast.h
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Original file line number Diff line number Diff line change
Expand Up @@ -33,9 +33,9 @@ using Expression = std::variant<CallExpr, StringLiteral, Identifier, ListComp, L
struct Argument;

struct CallExpr {
std::string target;
std::shared_ptr<Expression> target;
std::vector<Argument> args;
constexpr bool operator==(CallExpr const &) const = default;
constexpr bool operator==(CallExpr const &) const;
};

struct DictExpr {
Expand Down Expand Up @@ -64,6 +64,10 @@ struct Argument {
constexpr bool operator==(Argument const &) const = default;
};

constexpr bool CallExpr::operator==(CallExpr const &o) const {
return *target == *o.target && args == o.args;
}

constexpr bool DictExpr::operator==(DictExpr const &o) const { return entries == o.entries; }

constexpr bool ListComp::operator==(ListComp const &o) const {
Expand Down
54 changes: 32 additions & 22 deletions starlark/parser.h
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Expand Up @@ -99,28 +99,8 @@ class Parser {

void reconsume(Token token) { peeked_token_ = std::move(token); }

std::optional<Expression> parse_expression(Token &token) {
std::optional<Expression> parse_operand(Token &token) {
if (auto const *ident = std::get_if<token::Identifier>(&token)) {
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::move(ident->name),
.args = std::move(*args),
};
}

if (next) {
reconsume(std::move(*next));
}

return Identifier{.name = std::move(ident->name)};
}

Expand Down Expand Up @@ -283,10 +263,40 @@ class Parser {
return DictExpr{.entries = std::move(entries)};
}

std::cerr << "Unexpected token in expression: " << to_string(token) << ".\n";
std::cerr << "Unexpected token in operand: " << to_string(token) << ".\n";
return std::nullopt;
}

std::optional<Expression> parse_expression(Token &token) {
auto operand = parse_operand(token);
if (!operand) {
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),
};
}

if (next) {
reconsume(std::move(*next));
}

return operand;
}

std::optional<std::vector<Argument>> parse_argument_list() {
std::vector<Argument> args;

Expand Down
31 changes: 26 additions & 5 deletions starlark/parser_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,8 @@ int main() {
starlark::ExpressionStmt{
.expr{
starlark::CallExpr{
.target = "foo",
.target = std::make_shared<starlark::Expression>(
starlark::Identifier{"foo"}),
.args{
{
starlark::Identifier{"bar"},
Expand All @@ -95,7 +96,8 @@ int main() {
starlark::ExpressionStmt{
.expr{
starlark::CallExpr{
.target = "foo",
.target = std::make_shared<starlark::Expression>(
starlark::Identifier{"foo"}),
.args{
{
starlark::Identifier{"bar"},
Expand All @@ -104,7 +106,8 @@ int main() {
{
std::nullopt,
starlark::CallExpr{
.target = "qux",
.target = std::make_shared<starlark::Expression>(
starlark::Identifier{"qux"}),
.args{},
},
},
Expand All @@ -126,7 +129,8 @@ int main() {
starlark::StringLiteral{"foo"},
starlark::Identifier{"bar"},
starlark::CallExpr{
.target = "baz",
.target = std::make_shared<starlark::Expression>(
starlark::Identifier{"baz"}),
.args{},
},
},
Expand All @@ -150,7 +154,8 @@ int main() {
},
{
starlark::CallExpr{
.target = "baz",
.target = std::make_shared<starlark::Expression>(
starlark::Identifier{"baz"}),
.args{},
},
starlark::StringLiteral{"qux"},
Expand Down Expand Up @@ -228,6 +233,22 @@ int main() {
},
},
},
{
R"("foo"())",
starlark::Program{
.statements{
starlark::ExpressionStmt{
.expr{
starlark::CallExpr{
.target = std::make_shared<starlark::Expression>(
starlark::StringLiteral{"foo"}),
.args{},
},
},
},
},
},
},
});

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