[m-rev.] For review: State Variables

[Simon Taylor]

On 25-Jun-2002, Ralph Becket <rafe at cs.mu.OZ.AU> wrote:
> diff -u make_hlds.m make_hlds.m
> --- make_hlds.m	7 Jun 2002 07:39:12 -0000
> +++ make_hlds.m	25 Jun 2002 06:45:05 -0000
> @@ -16,9 +16,6 @@
>  % super-homogenous form, and introduce implicit quantification.
>  % 
>  % XXX we should record each error using module_info_incr_errors.
> -%
> -% XXX For state variables, we should allow quantifiers around if-then-else
> -% expressions.

You still haven't handled quantification for if-then-else goals.
It's fine to do that as a separate change immediately after you commit.

> +	% We implement a special purpose comparison for state variable
> +	% names that compares the numbers appended at the right hand
> +	% ends of the name strings.
> +	%
> +	% NOTE state variable names are either "..._X" or "..._X_N"
> +	% where X is the name of the program variable used for the
> +	% state variable and N is a decimal number with no leading
> +	% zeroes.
> +	%
> +:- pred compare_svar_names(comparison_result, string, string).
> +:- mode compare_svar_names(out, in, in) is det.
> +
> +compare_svar_names(R, A, B) :-
> +	csvns_1(R, 1, A, length(A), B, length(B)).

> +	% First find the start of the numbers at the right hand end, if
> +	% present.
> +	%
> +:- pred csvns_1(comparison_result, int, string, int, string, int).
> +:- mode csvns_1(out, in, in, in, in, in) is det.

Please don't abbreviate like that.

> +csvns_1(R, I, A, MaxA, B, MaxB) :-
> +	( if I < MaxA, I < MaxB then
> +		X = A `unsafe_index` (MaxA - I),
> +		Y = B `unsafe_index` (MaxB - I),
> +		( if is_digit(X), is_digit(Y)      then
> +			csvns_1(R, I + 1, A, MaxA, B, MaxB)
> +		  else if X = ('_'),   is_digit(Y) then
> +		  	R = (<)
> +		  else if is_digit(X), Y = ('_')   then
> +		  	R = (>)
> +		  else if X = ('_'),   Y = ('_')   then
> +		  	csvns_2(R, I - 1, A, MaxA, B, MaxB)
> +		  else if X = Y                    then
> +		  	R = (=)
> +		  else
> +			error("make_hlds__compare_svar_names: \
> +names are not in expected format")
> +		)
> +	  else
> +		error("make_hlds__compare_svar_names: \
> +names are not in expected format")
> +	).
> +
> +
> +	% Decide the greater of the two numbers at the right hand end
> +	% (both numbers will have the same number of digits.)
> +	%
> +:- pred csvns_2(comparison_result, int, string, int, string, int).
> +:- mode csvns_2(out, in, in, in, in, in) is det.
> +
> +csvns_2(R, I, A, MaxA, B, MaxB) :-
> +	( if 0 < I then
> +		X = A `unsafe_index` (MaxA - I) `with_type` char,
> +		Y = B `unsafe_index` (MaxB - I) `with_type` char,
> +		compare(RXY, X, Y),
> +		(	RXY = (<),	R = (<)
> +		;	RXY = (=),	csvns_2(R, I - 1, A, MaxA, B, MaxB)
> +		;	RXY = (>),	R = (>)
> +		)
> +	  else
> +	  	R = (=)
> +	).

This looks over-complicated to me. Wouldn't it be simpler to
write a predicate to parse the trailing integer of a string,
and then just compare the results.

Simon.
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