[m-dev.] for review: fixing formatting of HLDS dumps

[Fergus Henderson]

On 18-Feb-1999, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> On 18-Feb-1999, Zoltan Somogyi <zs at cs.mu.OZ.AU> wrote:
> > +++ prog_out.m	1999/02/18 06:21:08
> > @@ -40,6 +40,9 @@
> >  :- pred prog_out__write_sym_name(sym_name, io__state, io__state).
> >  :- mode prog_out__write_sym_name(in, di, uo) is det.
> >  
> > +:- pred prog_out__write_quoted_sym_name(sym_name, io__state, io__state).
> > +:- mode prog_out__write_quoted_sym_name(in, di, uo) is det.
> 
> I think it might be better to just change the behaviour of
> prog_out__write_sym_name.  Is there ever any reason to
> write out a sym_name not properly quoted?

To answer my own question: yes.  In particular, when writing out error
messages, we already put the sym_name inside a back/forward-quote pair
`...', so adding a forward-quote pair '...' would leave you with `'...'',
which is horrible.  So having a separate prog_out__write_sym_name and
prog_out__write_quoted_sym is correct.

However, even when writing out error messages, we still ought to escape
any special characters.  For example, if you by mistake write

	:- func newline = char.
	newline = '\n '.
		%    ^ oops

then the error message that you currently get is very ugly,

	foo.m:001: In clause for function `foo:x/0':
	foo.m:001:   in argument 1 of clause head:
	foo.m:001:   error: undefined symbol `
	 /0'.

and can't even be parsed properly by utilites such as emacs, error,
vim -e, etc.  It would be better, IMHO, to use an error message
like this:

	...
	foo.m:001:   error: undefined symbol `\n /0'.

(Trying to print out the symbol name in quotes, i.e.

	foo.m:001:   error: undefined symbol `'\n '/0'.

would be worse, IMHO.)

So I think prog_out__write_sym_name should be changed to call
term_io__write_escaped_string, while the new prog_out__write_quoted_string
that you have added should call term_io__write_atom.

Some comments are needed.  I suggest the following:

	% Write out a symbol name, with special characters escaped,
	% but without any quotes.  This is suitable for use in
	% error messages, where the caller should print out an
	% enclosing forward/backward-quote pair (`...').
	:- pred prog_out__write_sym_name(sym_name, io__state, io__state).
	:- mode prog_out__write_sym_name(in, di, uo) is det.

	% Write out a symbol name, enclosed in single forward quotes ('...')
	% if necessary, and with any special characters escaped.
	% The output should be a syntactically valid Mercury term.
	:- pred prog_out__write_quoted_sym_name(sym_name, io__state, io__state).
	:- mode prog_out__write_quoted_sym_name(in, di, uo) is det.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "Binaries may die
WWW: <http://www.cs.mu.oz.au/~fjh>  |   but source code lives forever"
PGP: finger fjh at 128.250.37.3        |     -- leaked Microsoft memo.