LineDirective

To aid in the debugging of code produced by program generators such as Noweb, MLton supports comments with line directives of the form ` (#line _line_._col_ "_file_"). Here, _line_ and _col_ are sequences of decimal digits and _file_ is the source file. The first character of a source file has the position 1.1. A line directive causes the front end to believe that the character following the right parenthesis is at the line and column of the specified file. A line directive only affects the reporting of error messages and does not affect program semantics (except for functions like `MLton.Exn.history that report source file positions). Syntactically invalid line directives are ignored. To prevent incompatibilities with SML, the file name may not contain the character sequence *).