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//! The type sub-grammar.
//!
//! These are methods on the one and only [`Parser`]: they share the lexer,
//! token cursor, `ParseError` channel and span infrastructure with expression
//! parsing, but they never re-enter the Pratt expression parser. Monkey has no
//! typed/untyped mode switch — annotations are optional syntax inside ordinary
//! `.monkey` source, and every type position is introduced by a preceding `:`
//! (or by the structure of an enclosing type), so no backtracking is needed.
use crate::ast::*;
use crate::{ParseError, Parser};
use lexer::token::{Span, TokenKind};
impl Parser<'_> {
/// Parses `: T` starting from the token *before* the `:`.
pub(crate) fn parse_type_annotation(&mut self) -> Result<TypeAnnotation, ParseError> {
self.expect_peek(&TokenKind::COLON)?;
self.next_token();
return self.parse_type();
}
/// Consumes `: T` when the peek token is a `:`, otherwise yields `None`.
pub(crate) fn parse_optional_type_annotation(
&mut self,
) -> Result<Option<TypeAnnotation>, ParseError> {
if !self.peek_token_is(&TokenKind::COLON) {
return Ok(None);
}
return Ok(Some(self.parse_type_annotation()?));
}
/// `type ::= postfix_type`. Assumes the current token starts the type.
pub(crate) fn parse_type(&mut self) -> Result<TypeAnnotation, ParseError> {
let mut annotation = self.parse_primary_type()?;
// `?` is postfix and binds tightest; `T??` normalizes to `T?`.
while self.peek_token_is(&TokenKind::QUESTION) {
self.next_token();
let span = Span {
start: annotation.span().start,
end: self.current_token.span.end,
};
annotation = match annotation {
// Already optional: only the cover span grows to swallow the
// extra `?`, so tooling that slices spans sees `T??`, not `T?`.
already @ TypeAnnotation::Optional(_) => with_span(already, span),
inner => TypeAnnotation::Optional(OptionalType {
inner: Box::new(inner),
span,
}),
};
}
return Ok(annotation);
}
fn parse_primary_type(&mut self) -> Result<TypeAnnotation, ParseError> {
match &self.current_token.kind {
TokenKind::IDENTIFIER {
name,
} => {
return Ok(TypeAnnotation::Named(NamedType {
name: name.clone(),
span: self.current_token.span.clone(),
}))
}
TokenKind::LBRACKET => {
let start = self.current_token.span.start;
self.next_token();
let element = self.parse_type()?;
self.expect_peek(&TokenKind::RBRACKET)?;
return Ok(TypeAnnotation::Array(ArrayType {
element: Box::new(element),
span: Span {
start,
end: self.current_token.span.end,
},
}));
}
TokenKind::LBRACE => {
let start = self.current_token.span.start;
self.next_token();
let key = self.parse_type()?;
self.expect_peek(&TokenKind::COLON)?;
self.next_token();
let value = self.parse_type()?;
self.expect_peek(&TokenKind::RBRACE)?;
return Ok(TypeAnnotation::Hash(HashType {
key: Box::new(key),
value: Box::new(value),
span: Span {
start,
end: self.current_token.span.end,
},
}));
}
TokenKind::FUNCTION => {
let start = self.current_token.span.start;
self.expect_peek(&TokenKind::LPAREN)?;
let params = self.parse_type_list()?;
// A function *type* must spell out its return type; that is what
// keeps `{fn(int): int: bool}` unambiguous without backtracking.
if !self.peek_token_is(&TokenKind::COLON) {
return Err("function type requires a return type".to_string());
}
let return_type = self.parse_type_annotation()?;
return Ok(TypeAnnotation::Function(FunctionType {
params,
span: Span {
start,
end: return_type.span().end,
},
return_type: Box::new(return_type),
}));
}
TokenKind::LPAREN => {
// Grouping produces no node of its own; it only widens the cover
// span of the type it wraps.
let start = self.current_token.span.start;
self.next_token();
let inner = self.parse_type()?;
self.expect_peek(&TokenKind::RPAREN)?;
let span = Span {
start,
end: self.current_token.span.end,
};
return Ok(with_span(inner, span));
}
_ => {
return Err(format!("expected a type, got: {}", self.current_token));
}
}
}
/// `type_list ::= ( type ( "," type )* )?`, consuming through the `)`.
/// Assumes the current token is the opening `(`.
fn parse_type_list(&mut self) -> Result<Vec<TypeAnnotation>, ParseError> {
let mut types = Vec::new();
if self.peek_token_is(&TokenKind::RPAREN) {
self.next_token();
return Ok(types);
}
self.next_token();
types.push(self.parse_type()?);
while self.peek_token_is(&TokenKind::COMMA) {
self.next_token();
self.next_token();
types.push(self.parse_type()?);
}
self.expect_peek(&TokenKind::RPAREN)?;
return Ok(types);
}
}
/// Replaces a type's span with the cover span of its enclosing parentheses.
fn with_span(annotation: TypeAnnotation, span: Span) -> TypeAnnotation {
match annotation {
TypeAnnotation::Named(mut inner) => {
inner.span = span;
TypeAnnotation::Named(inner)
}
TypeAnnotation::Array(mut inner) => {
inner.span = span;
TypeAnnotation::Array(inner)
}
TypeAnnotation::Hash(mut inner) => {
inner.span = span;
TypeAnnotation::Hash(inner)
}
TypeAnnotation::Function(mut inner) => {
inner.span = span;
TypeAnnotation::Function(inner)
}
TypeAnnotation::Optional(mut inner) => {
inner.span = span;
TypeAnnotation::Optional(inner)
}
}
}