Crap, and stuff.

thun/crap-n-stuff.txt

@@ -0,0 +1,93 @@
+
+
+combo(branch, [T, F,  Expr|S], S, Ei, Eo) :-
+    \+ Expr = true, \+ Expr = false,
+    catch(  % Try Expr and do one or the other,
+        (Expr -> append(T, Ei, Eo) ; append(F, Ei, Eo)),
+        _,  % If Expr don't grok, try both branches.
+        (append(T, Ei, Eo) ; append(F, Ei, Eo))
+        ).
+
+combo(loop, [B,  Expr|S], S, Ei, Eo) :-
+    \+ Expr = true, \+ Expr = false,
+    catch(  % Try Expr and do one or the other,
+        (Expr -> append(B, [B, loop|Ei], Eo) ; Ei=Eo),
+        _,  % If Expr don't grok, try both branches.
+        (Ei=Eo ; append(B, [B, loop|Ei], Eo))
+        ).
+
+/*
+
+To handle comparision operators the possibility of exceptions due to
+insufficiently instantiated arguments must be handled.  First try to make
+the comparison and set the result to a Boolean atom.  If an exception
+happens just leave the comparison expression as the result and some other
+function or combinator will deal with it.  Example:
+
+    func(>,  [A, B|S], [C|S]) :- catch(
+            (B > A -> C=true ; C=false),
+            _,
+            C=(B>A)  % in case of error.
+            ).
+
+To save on conceptual overhead I've defined a term_expansion/2 that sets
+up the func/3 for each op.
+*/
+
+term_expansion(comparison_operator(X), (func(X, [A, B|S], [C|S]) :-
+    F =.. [X, B, A], catch((F -> C=true ; C=false), _, C=F))).
+
+% I don't use Prolog-compatible op symbols in all cases.
+term_expansion(comparison_operator(X, Y), (func(X, [A, B|S], [C|S]) :-
+    F =.. [Y, B, A], catch((F -> C=true ; C=false), _, C=F))).
+
+% Likewise for math operators, try to evaluate, otherwise use the
+% symbolic form.
+
+term_expansion(math_operator(X), (func(X, [A, B|S], [C|S]) :-
+    F =.. [X, B, A], catch(C is F, _, C=F))).
+
+term_expansion(math_operator(X, Y), (func(X, [A, B|S], [C|S]) :-
+    F =.. [Y, B, A], catch(C is F, _, C=F))).
+
+
+
+% Symbolic math expressions are literals.
+literal(_+_).
+literal(_-_).
+literal(_*_).
+literal(_/_).
+literal(_ mod _).
+
+% Symbolic comparisons are literals.
+literal(_>_).
+literal(_<_).
+literal(_>=_).
+literal(_=<_).
+literal(_=:=_).
+literal(_=\=_).
+
+
+
+% Symbolic math.  Compute the answer, or derivative, or whatever, later.
+math_operator(+).
+math_operator(-).
+math_operator(*).
+math_operator(/).
+math_operator(mod).
+
+% Attempt to calculate the value of a symbolic math expression.
+func(calc, [A|S], [B|S]) :- B is A.
+
+func(sqrt, [A|S], [sqrt(A)|S]).
+
+
+comparison_operator(>).
+comparison_operator(<).
+comparison_operator(>=).
+comparison_operator(<=, =<).
+comparison_operator(=, =:=).
+comparison_operator(<>, =\=).
+
+
+