From 714bf2cab6f1e7bd91d332c13682645d89cf340c Mon Sep 17 00:00:00 2001
From: Simon Forman <sforman@hushmail.com>
Date: Sat, 20 Jul 2019 16:45:28 -0700
Subject: [PATCH] Try to handle expressions in branch combinator.

If the expression isn't 'true' or 'false' atoms then we assume it's a comparison expression and try to check its truth value.

If this fails then it will try both branches, to allow for e.g. compilation.  THis almost works, but there's a choice point or something that gets hit before it tries the false path,

?- joy(` [32 >] [++] [--] ifte`, Si, So).
Si = [_2076|_2078],
So = [_2076+1|_2078] ;
wtf? +
Si = [_2076|_2078],
So = [[+], 1, _2076|_2078] ;
Si = [_2076|_2078],
So = [_2076-1|_2078] ;
wtf? -
Si = [_2076|_2078],
So = [[-], 1, _2076|_2078] ;
wtf? branch
Si = [_2076|_2078],
So = [[branch], [++], [--], _2076>32, _2076|_2078] ;
wtf? swap
Si = [_2076|_2078],
So = [[swap, branch], [--], [++], _2076>32, _2076|_2078] ;
wtf? first
Si = [_2076|_2078],
So = [[first, [++], [--], swap, branch], [_2076>32|_2078], _2076|_2078]


etc...
---
 thun/thun.pl | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/thun/thun.pl b/thun/thun.pl
index bd98254..b235003 100644
--- a/thun/thun.pl
+++ b/thun/thun.pl
@@ -192,8 +192,15 @@ combo(dipd, [P, X, Y|S], S, Ei, Eo) :- append(P, [Y, X|Ei], Eo).
 
 combo(dupdip, [P, X|S], [X|S], Ei, Eo) :- append(P, [X|Ei], Eo).
 
-combo(branch, [T, _,  true|S], S, Ei, Eo) :- append(T, Ei, Eo).
-combo(branch, [_, F, false|S], S, Ei, Eo) :- append(F, Ei, Eo).
+combo(branch, [T, _,  true|S], S, Ei, Eo) :- !, append(T, Ei, Eo).
+combo(branch, [_, F, false|S], S, Ei, Eo) :- !, append(F, Ei, Eo).
+combo(branch, [T, F,  Expr|S], S, Ei, Eo) :-
+    catch(
+        (Expr -> append(T, Ei, Eo) ; append(F, Ei, Eo)),
+        _,
+        try_both_branches(T, F, Ei, Eo)  % in case of error.
+        ).
+
 
 combo(loop, [_, false|S], S, E,  E ).
 combo(loop, [B,  true|S], S, Ei, Eo) :- append(B, [B, loop|Ei], Eo).
@@ -213,6 +220,10 @@ combo(genrec, [R1, R0, Then, If|S],
     append(R0, [Quoted|R1], Else).
 
 
+try_both_branches(T, _, Ei, Eo) :- append(T, Ei, Eo).
+try_both_branches(_, F, Ei, Eo) :- append(F, Ei, Eo).
+
+
 /*
 Compiler
 */