truly fork, sort of

thun/gnu-prolog/Makefile

@@ -2,7 +2,7 @@
 GPLC_OPTIONS=--no-top-level
 #GPLC_OPTIONS=
 
-THUN_DEPS=parser.pl defs.pl main.pl math.pl DCG_basics.pl
+THUN_DEPS=parser.pl defs.pl main.pl math.pl DCG_basics.pl fork.pl
 
 thun: thun.pl $(THUN_DEPS) Makefile
 	gplc $(GPLC_OPTIONS) -o thun thun.pl $(THUN_DEPS)
@@ -11,6 +11,7 @@ defs.pl: meta-defs.pl parser.pl defs.txt thun.pl DCG_basics.pl
 	gprolog \
 		--consult-file meta-defs.pl \
 		--consult-file parser.pl \
+		--consult-file fork.pl \
 		--consult-file thun.pl \
 		--consult-file DCG_basics.pl \
 		--query-goal do

thun/gnu-prolog/defs.pl

@@ -20,7 +20,6 @@ def(drop,[[rest],times]).
 def(dupdd,[[dup],dipd]).
 def(dupdipd,[dup,dipd]).
 def(enstacken,[stack,[clear],dip]).
-def(fork,[[i],app2]).
 def(fourth,[rest,third]).
 def(gcd,[true,[tuck,mod,dup,0,>],loop,pop]).
 def(grabN,[[],swap,[cons],times]).

thun/gnu-prolog/defs.txt

@@ -22,7 +22,6 @@ dupdd == [dup] dipd
 dupdipd == dup dipd
 enstacken == stack [clear] dip
 flatten == [] swap [concat] step
-fork == [i] app2
 fourth == rest third
 gcd == true [tuck mod dup 0 >] loop pop
 grabN == [] swap [cons] times

thun/gnu-prolog/fork.pl

@@ -0,0 +1,41 @@
+:- multifile(func/3).
+
+func(fork, [F, G|S], [X, Y|S]) :-
+    fork(F, S, X, ChildPID),
+    thun(G, S, [Y|_]),
+    wait(ChildPID, Status).  % FIXME check status!!!
+
+fork(Expr, Stack, Result, ChildPID) :-
+    mkpipe(In, Out),
+    fork_prolog(ChildPID),
+    bar(ChildPID, In, Out, Expr, Stack, Result).
+
+bar(0, In, Out, Expr, Stack, Result) :-
+    close(In),
+    thun(Expr, Stack, [Result|_]),
+    w(Out, Result),
+    close(Out),
+    halt.
+
+bar(P, In, Out, Expr, Stack, Result) :-
+    integer(P), P =\= 0,
+    close(Out),
+    select([In], R, [], _, 1500),
+    (R=[In] ->
+        read(In, Result)
+    ;
+        Result=timeout
+    ),
+    close(In).
+
+mkpipe(In, Out) :-
+    create_pipe(In, Out),
+    set_stream_buffering(Out, none),
+    set_stream_buffering(In, none).
+
+w(Out, Term) :-          % To get a term written out and recognized,
+    write(Out, Term),    % you write it to the stream
+    put_code(Out, 0'.),  % add a period at the end
+    nl(Out),             % and a newline even if you set buffering
+    flush_output(Out).   % to none, then flush for good measure.
+