[m-rev.] for review: anon_var_info

[Julien Fischer]

On Mon, 19 Jun 2023, Zoltan Somogyi wrote:

> Support two ways to write unnamed vars.
> 
> library/term_io.m:
>     Replace the !N threaded through the code writing out terms, which was
>     used only in commented-out code, with a value of a new type,
>     anon_var_info, being threaded through. The two values of this type
>     each choose one of two ways to write out unnamed variables.
>     This capability is not yet exposed to users.
> 
> diff --git a/library/term_io.m b/library/term_io.m
> index b5426035b..138482fa9 100644
> --- a/library/term_io.m
> +++ b/library/term_io.m
> @@ -46,13 +46,14 @@
>  :- pred write_term_with_op_table(io.text_output_stream::in, OpTable::in,
>      varset(T)::in, term(T)::in, io::di, io::uo) is det <= op_table(OpTable).
> 
> -    % As above, except it appends a period and new-line.
> +    % As write_term, except it appends a period and a newline character.

I would delete character since on some systems a newline is multiple characters.

>      %
>  :- pred write_term_nl(varset(T)::in, term(T)::in, io::di, io::uo) is det.
>  :- pred write_term_nl(io.text_output_stream::in, varset(T)::in, term(T)::in,
>      io::di, io::uo) is det.
> 
> -    % As above, except it appends a period and new-line.
> +    % As write_term_with_op_table above, except it appends a period
> +    % and a newline character.

Ditto.

>      %
>  :- pred write_term_nl_with_op_table(OpTable::in,
>      varset(T)::in, term(T)::in, io::di, io::uo) is det <= op_table(OpTable).
> @@ -276,7 +278,8 @@ write_term_with_op_table(OpTable, VarSet, Term, !IO) :-
>      write_term_with_op_table(OutStream, OpTable, VarSet, Term, !IO).
>
>  write_term_with_op_table(OutStream, OpTable, VarSet, Term, !IO) :-
> -    write_term_anon_vars(OutStream, OpTable, Term, VarSet, _, 0, _, !IO).
> +    write_term_anon_vars(OutStream, OpTable, Term, VarSet, _,
> +        anon_var_to_int, _, !IO).
>
>  %---------------------%
>

...


> @@ -701,7 +711,20 @@ write_variable_with_op_table(OpTable, Var, VarSet, !IO) :-
>      write_variable_with_op_table(OutStream, OpTable, Var, VarSet, !IO).
>
>  write_variable_with_op_table(OutStream, OpTable, Var, VarSet, !IO) :-
> -    write_variable_anon_vars(OutStream, OpTable, Var, VarSet, _, 0, _, !IO).
> +    write_variable_anon_vars(OutStream, OpTable, Var, VarSet, _,
> +        anon_var_to_int, _, !IO).
> +
> +:- type anon_var_info
> +    --->    anon_var_to_int
> +            % The string we use to write out an anonymous variable
> +            % should be derived from its variable number, obtained
> +            % by calling var_to_int on it.
> +    ;       anon_occur_order(counter).
> +            % The string we use to write out an anonymous variable
> +            % should be based on whether it is the first, second, third etc
> +            % anonymous variable that our traversal of the whole term
> +            % has encountered. The counter tells us the number we should give
> +            % to the *next* one we encounter.
>
>      % Write a variable.
>      %
> @@ -709,49 +732,58 @@ write_variable_with_op_table(OutStream, OpTable, Var, VarSet, !IO) :-
>      %
>      % 1 Convert the variable to the integer that represents it and write
>      %   `_N' where N is that integer. This has the advantage that
> -    %    such variables get printed in a canonical way, so rearranging terms
> -    %    containing such variables will not effect the way they are numbered
> -    %    (this includes breaking up a term and printing the pieces separately).
> +    %   such variables get printed in a canonical way, so rearranging terms
> +    %   containing such variables will not effect the way they are numbered

s/effect/affect/

The diff looks fine otherwise.

Julien.