init filename lexbuf initializes the lexing buffer lexbuf so that the positions that are subsequently read from it refer to the file filename. It returns lexbuf.

read filename reads the entire contents of the file filename and returns a pair of this content (a string) and a lexing buffer that has been initialized, based on this string.

newline lexbuf increments the line counter stored within lexbuf. It should be invoked by the lexer itself every time a newline character is consumed. This allows maintaining a current the line number in lexbuf.

range (startpos, endpos) prints a textual description of the range delimited by the start and end positions startpos and endpos. This description is one line long and ends in a newline character. This description mentions the file name, the line number, and a range of characters on this line. The line number is correct only if newline has been correctly used, as described dabove.

tabulate is_eof lexer tabulates the lexer lexer: that is, it immediately runs this lexer all the way until an EOF token is found, stores the tokens in an array in memory, and returns a new lexer which (when invoked) reads tokens from this array. The function lexer is not allowed to raise an exception, and must produce a finite stream of tokens: that is, after a finite number of invocations, it must return a token that is identified by the function is_eof as an EOF token.

Both the existing lexer lexer and the new lexer returned by tabulate is_eof lexer are functions of type unit -> 'a, where the type 'a is likely to be instantiated with a triple of a token and two positions, as per the revised lexer API described in the module Convert.