Experiment with putting logic vars on the stack.

thun/gnu-prolog/defs.pl

@@ -28,6 +28,7 @@ def(grba,[[stack,popd],dip]).
 def(hypot,[[sqr],ii,+,sqrt]).
 def(ifte,[[nullary],dipd,swap,branch]).
 def(ii,[[dip],dupdip,i]).
+def(infer,[thunk,dup,rollup,infra]).
 def(infra,[swons,swaack,[i],dip,swaack]).
 def(infrst,[infra,first]).
 def(least_fraction,[dup,[gcd],infra,[div],concat,map]).

thun/gnu-prolog/defs.txt

@@ -30,6 +30,7 @@ grba == [stack popd] dip
 hypot == [sqr] ii + sqrt
 ifte == [nullary] dipd swap branch
 ii == [dip] dupdip i
+infer == thunk dup rollup infra
 infra == swons swaack [i] dip swaack
 infrst == infra first
 least_fraction == dup [gcd] infra [div] concat map

thun/gnu-prolog/parser.pl

@@ -100,8 +100,10 @@ format_joy([T])   --> format_term(T), !.
 format_joy([T|S]) --> format_term(T), " ", format_joy(S).
 format_joy([])    --> [].
 
-format_term(N) --> {number(N), number_codes(N, Codes)}, Codes.
-format_term(A) --> {  atom(A),   atom_codes(A, Codes)}, Codes.
+format_term(N) --> {number(N),   number_codes(N, Codes)}, Codes.
+format_term(A) --> {  atom(A),     atom_codes(A, Codes)}, Codes.
+format_term(V) --> {   var(V), write_to_codes(Codes, V)}, Codes.
 format_term([A|As]) --> "[", format_joy([A|As]), "]".
+format_term(F) --> {    write_to_codes(Codes, F)}, Codes.
 
 

thun/gnu-prolog/thun.pl

@@ -91,6 +91,7 @@ func(clear,        _ ,      []).
 func(first, [[X|_]|S],   [X|S]).
 func(rest,  [[_|X]|S],   [X|S]).
 func(unit,      [X|S], [[X]|S]).
+func(thunk,        S ,   [X|S]).
 
 func(rolldown, [A, B, C|S], [B, C, A|S]).
 func(dupd,        [A, B|S], [A, B, B|S]).