[hcoop/debian/mlton.git] / doc / guide / src / LineDirective.adoc

LineDirective
=============

To aid in the debugging of code produced by program generators such
as http://www.eecs.harvard.edu/%7Enr/noweb/[Noweb], MLton supports
comments with line directives of the form
[source,sml]
----
(*#line l.c "f"*)
----
Here, _l_ and _c_ are sequences of decimal digits and _f_ 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 `*)`.
Commit	Line	Data
7f918cf1 CE	1	LineDirective
	2	=============
	3
	4	To aid in the debugging of code produced by program generators such
	5	as http://www.eecs.harvard.edu/%7Enr/noweb/[Noweb], MLton supports
	6	comments with line directives of the form
	7	[source,sml]
	8	----
	9	(#line l.c "f")
	10	----
	11	Here, _l_ and _c_ are sequences of decimal digits and _f_ is the
	12	source file. The first character of a source file has the position
	13	1.1. A line directive causes the front end to believe that the
	14	character following the right parenthesis is at the line and column of
	15	the specified file. A line directive only affects the reporting of
	16	error messages and does not affect program semantics (except for
	17	functions like `MLton.Exn.history` that report source file positions).
	18	Syntactically invalid line directives are ignored. To prevent
	19	incompatibilities with SML, the file name may not contain the
	20	character sequence `*)`.