Eleminating left recursion in parser rule of spirit x3

Question

I am currently stuck with a rule I am trying to parse using boost spirit x3. Here is the EBNF(using the % operator from spirit for lists) for what I am trying to parse:

Answer 1

I solved this problem and the solution was incredibly easy. The trick is to change the grammar, so I dont have a left recursion, and it parses nice into my structs.

so I changed

type ::= class_type | lambda_type

lambda_type ::= more_arg_lambda | one_arg_lambda

more_arg_lambda ::= "(", type%",", ")", "=>", type

one_arg_lambda ::= type, "=>", type  <- here is the left recursion

class_type ::= identifier%"::", ["<", type%",", ">"]

to

type ::= class_type | lambda_type

lambda_type ::= more_arg_lambda | one_arg_lambda

more_arg_lambda ::= "(", type%",", ")", "=>", type

one_arg_lambda ::= class_type, "=>", type  <- here is the magic trick

class_type ::= identifier%"::", ["<", type%",", ">"]

this second grammar descripes the exaclty same language, but without left recursion, and without changing the structure of the grammar. This was actualy luck and doesnt work for every grammar obviously.