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From: Mild Shock <janburse@fastmail.fm>
Newsgroups: comp.lang.prolog
Subject: Re: How Prolog became an education nightmare (Was: 50 Years of Prolog
 Nonsense)
Date: Tue, 12 Nov 2024 16:32:44 +0100
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Here is the SWI-Prolog and the SICStus
Prolog abstract parse term. This is the real
nightmare of every computer science professor,

who wants to use Prolog in a compiler
construction course:

/* SWI-Prolog 9.3.14 */
end(end(begin(;(=(x,1),;(=(y,2),begin(=(z,3)))))))

/* SICStus Prolog 4.9.0 */
begin(;(=(x,1),;(=(y,2),begin(end(end(=(z,3)))))))

On the other hand mostlikely the OP @horsh
would expect:

/* What the End-User wants */
end(begin(;(=(x,1),;(=(y,2),end(begin(=(z,3)))))))

I think its impossible to do in any Prolog system,
you would need a programming language with the
possibility to do mixfix syntax definitions,

like for example in Isabelle/HOL:

(* Define the mixfix syntax for a Pascal-like block *)
syntax
   "_begin_end" :: "'a ⇒ 'a" ("begin _ end")

Or otherwise use DCG to write your own parser
for the DSL at hand, that you want to parse.
Since Prolog operators cannot model mixfix syntax,

at least SWI-Prolog and SICStus Prolog fail,
and I guess other Prolog systems fail as well.

Mild Shock schrieb:
> Concerning the input (xxx yyy zzz) the OP wrote:
> 
> I would expect it to print zzz(xxx(yyy)).
> 
> Where did he get this requirement from, he didn’t
> compare other Prolog systems, right? So it came from
> his applicationdomain. But what was his application
> 
> domain? Ok, lets proceed to an example with multiple
> brakets. Lets make the Pascal “begin” “end” example,
> by replacing xxx and zzz by “begin” and “end”.
> 
> I get this result:
> 
> ?- member(X,[begin,end]), current_op(Y,Z,X).
> X = (begin), Y = 1100, Z = fy ;
> X = (end), Y = 1100, Z = yf.
> 
> ?- X = (begin
> |          x = 1;
> |          y = 2;
> |          begin
> |               z = 3
> |          end
> |       end).
> X = (begin x=1;y=2;begin z=3 end end).
> 
> But is the abstract parse term, the Prolog result useful?
>