dictPair method
Implementation
Parser<({ExpressionNode? key, ExpressionNode val})> dictPair() => [
seq3(
ref0(singleExpression),
ref1(token, ':'),
ref0(singleExpression),
).map3((k, _, v) => (key: k, val: v)),
seq2(
ref1(token, '**'),
ref0(singleExpression),
).map2((_, v) => (key: null, val: v)),
].toChoiceParser();