[m-dev.] fix for bytecode generator

[Simon TAYLOR]

Hi Bert,

> Is it possible to avoid the test "FunctorList = [Char]"  by changing
> the declaration of sym_name prog_data.m to:
> 
> :- type sym_name 	---->	unqualified(string)	% Can remove?
> 			;	qualified(module_specifier, string)
> 			;	char_const(char).	% Added

If we were to add a specialised representation of characters, it would go
into the cons_id data type, as was done for byte_cons_id.

> This simplifies the code, but means changing other code that uses
> `unqualified(string)' to represent a char constant.

Should characters be treated differently to other enumeration types?
Currently the only places characters are treated separately are
code_util__cons_id_to_tag and bytecode_gen__map_cons_id. If we
did change the representation there would need to be a similar check
in the code to do the conversion during mode analysis (overloading
isn't resolved until after type-checking), so I don't think the change
would actually save much.

Simon.