Re: Any Prolog language lawyer out there?
From: Bart Demoen (bmd_at_cs.kuleuven.ac.be)
Date: 10/19/04
- Next message: Jan Wielemaker: "Re: Any Prolog language lawyer out there?"
- Previous message: Roberto Bagnara: "Any Prolog language lawyer out there?"
- In reply to: Roberto Bagnara: "Any Prolog language lawyer out there?"
- Next in thread: Jan Wielemaker: "Re: Any Prolog language lawyer out there?"
- Reply: Jan Wielemaker: "Re: Any Prolog language lawyer out there?"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Date: Tue, 19 Oct 2004 16:29:24 +0200
Roberto,
> Am I correct if I say that all the 6 tested systems are /not/ violating
> the ISO Prolog standard because unary plus is not mentioned in its Table 7
> (p. 19) and thus its presence and priority are implementation-defined?
> All the best,
>
> Roberto
>
> P.S. Standard or not standard, I find all this quite striking.
>
The + not figuring in ISO as fy, makes the situation murky. But - is in ISO as 200 fy.
And one finds differences like:
In SICStus:
| ?- prolog_flag(language,_,iso).
yes
| ?- current_op(200,fy,-).
yes
| ?- functor(- 4,X,Y).
X = -4,
Y = 0 ?
while GNU-Prolog says:
| ?- current_op(200,fy,-).
yes
| ?- functor(- 4,X,Y).
X = -
Y = 1
The old DEC-10 reader (used in e.g. SICStus) contains the clauses:
read(atom(-), L, [Token-_|S1], Precedence, Answer, Layout, S) :-
number_token(Token, Number), !,
Negative is -Number,
read_rest(S1, 0, Negative, L, Precedence, Answer, Layout, S).
read(atom(+), L, [Token-_|S1], Precedence, Answer, Layout, S) :-
number_token(Token, Number), !,
Negative is +Number,
read_rest(S1, 0, Negative, L, Precedence, Answer, Layout, S).
which seem to be responsible for the behaviour above. I think not ISO at all.
Moreover, if one retracts + as an operator, one should get syntax errors
for +4, but here is SICStus again:
| ?- op(0,fy,+).
yes
| ?- write(+4).
4
yes
while GNU says:
| ?- op(0,fy,+).
yes
| ?- write(+4).
uncaught exception: error(syntax_error('user_input:2 (char:8) , or ) expected'),read_term/3)
Cheers
Bart Demoen
- Next message: Jan Wielemaker: "Re: Any Prolog language lawyer out there?"
- Previous message: Roberto Bagnara: "Any Prolog language lawyer out there?"
- In reply to: Roberto Bagnara: "Any Prolog language lawyer out there?"
- Next in thread: Jan Wielemaker: "Re: Any Prolog language lawyer out there?"
- Reply: Jan Wielemaker: "Re: Any Prolog language lawyer out there?"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Relevant Pages
|
