How to unpack list parser to another list parser

[ykmnkmi]

Parser<Token> expressionStart = ...;
Parser<Token> expressionEnd = ...;
Parser<List<Token>> expressionBody = ...;
Parser<List<Object>> expression = expressionStart & expressionBody & expressionEnd;

and unpacking expression value to flat list

some thing like expressionStart & ...expressionBody & expressionEnd will be good

Parser<List<Token>> expression = expressionStart & expressionBody.unpack() & expressionEnd;

[renggli]

Not sure what you expect unpack() to do, but there is pick that returns the n-th element of a list:

Parser<List<Token>> expression = (expressionStart & expressionBody & expressionEnd)
    .pick(1);

[ykmnkmi]

my task is getting flatten list of tokens Parser<List<Token>> expression.
expressionStart and expressionEnd needed too.
Parser<List<Token>> expressionBody = ...; list of token
and i can't assign
Parser<List<Token>> expression = expressionStart & expressionBody & expressionEnd

(sorry for my poor english ☹)

[renggli]

This also includes the start and end tokens:

Parser<List<Token>> expression = (expressionStart & expressionBody & expressionEnd)
    .map((parts) => [parts[0], ...parts[1], parts[2]]);