Error

File "lexer.ml", line 14, characters 29-39:
Error: This expression has type 'a -> 'b
       but an expression was expected of type 'c Stream.t

lexer.ml

let rec lex = parser
    | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream
    | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] ->
            let buffer = Buffer.create 1 in
            Buffer.add_char buffer c;
            lex_ident buffer stream
    | [< ' ('0' .. '9' as c); stream >] ->
            let buffer = Buffer.create 1 in
            Buffer.add_char buffer c;
            lex_number buffer stream
    | [< ' ('#'); stream >] ->
            lex_comment stream
    | [< 'c; stream >] ->
            [< 'Token.Kwd c; lex stream >] <<<< ERROR HERE >>>>
    | [< >] -> [< >]
and lex_number buffer = parser
    | [< ' ('0' .. '9' | '.' as c); stream >] ->
            Buffer.add_char buffer c;
            lex_number buffer stream
    | [< stream=lex >] ->
            [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >]
and lex_ident buffer = parser
    | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] ->
            Buffer.add_char buffer c;
            lex_ident buffer stream
    | [< stream=lex >] ->
            match Buffer.contents buffer with
            | "def" -> [< 'Token.Def; stream >]
            | "extern" -> [< 'Token.Extern; stream >]
            | id -> [< 'Token.Ident id; stream >]
and lex_comment buffer <<<< WRONG ARG # HERE >>>> = parser
      | [< ' ('\n'); stream=lex >] -> stream
      | [< 'c; e=lex_comment >] -> e
      | [< >] -> [< >]