Function parseFnType

src/parser/syntaxes/types.ts:102–146

* ```abnf * FnType = "@" [TypeParams] "(" ParamTypes ")" "=>" Type * ParamTypes = [Type *(SEP Type)] * ```

(s: ITokenStream)

 * ```
*/
function parseFnType(s: ITokenStream): Ast.TypeSource {
	const startPos = s.getPos();

	s.expect(TokenKind.At);
	s.next();

	let typeParams: Ast.TypeParam[];
	if (s.is(TokenKind.Lt)) {
		typeParams = parseTypeParams(s);
	} else {
		typeParams = [];
	}

	s.expect(TokenKind.OpenParen);
	s.next();

	const params: Ast.TypeSource[] = [];
	while (!s.is(TokenKind.CloseParen)) {
		if (params.length > 0) {
			switch (s.getTokenKind()) {
				case TokenKind.Comma: {
					s.next();
					break;
				}
				case TokenKind.EOF: {
					throw new AiScriptUnexpectedEOFError(s.getPos());
				}
				default: {
					throw new AiScriptSyntaxError('separator expected', s.getPos());
				}
			}
		}
		const type = parseType(s);
		params.push(type);
	}

	s.expect(TokenKind.CloseParen);
	s.next();
	s.expect(TokenKind.Arrow);
	s.next();

	const resultType = parseType(s);

	return NODE('fnTypeSource', { typeParams, params, result: resultType }, startPos, s.getPos());
}

/**
 * ```abnf