support for X^[A,B] and X^length in arithmetic expressions.

C/eval.c

@@ -34,7 +34,54 @@ static char     SccsId[] = "%W% %G%";
 #include <unistd.h>
 #endif
 
+static Term Eval(Term t1 USES_REGS);
 
+static Term
+get_matrix_element(Term t1, Term t2 USES_REGS)
+{
+  if (!IsPairTerm(t2)) {
+    if (t2 == MkAtomTerm(AtomLength)) {
+      Int sz = 1;
+      while (IsApplTerm(t1)) {
+	Functor f = FunctorOfTerm(t1);
+	if (NameOfFunctor(f) != AtomNil) {
+	  return MkIntegerTerm(sz);
+	}
+	sz *= ArityOfFunctor(f);
+	t1 = ArgOfTerm(1, t1);
+      }
+      return MkIntegerTerm(sz);
+    }
+    Yap_ArithError(TYPE_ERROR_EVALUABLE, t2, "X is Y^[A]");
+    return FALSE;      
+  }
+  while (IsPairTerm(t2)) {
+    Int indx;
+    Term indxt = Eval(HeadOfTerm(t2) PASS_REGS);
+    if (!IsIntegerTerm(indxt)) {
+      Yap_ArithError(TYPE_ERROR_EVALUABLE, t2, "X is Y^[A]");
+      return FALSE;      
+    }
+    indx = IntegerOfTerm(indxt);
+    if (!IsApplTerm(t1)) {
+      Yap_ArithError(TYPE_ERROR_EVALUABLE, t1, "X is Y^[A]");
+      return FALSE;      
+    } else {
+      Functor f = FunctorOfTerm(t1);
+      if (ArityOfFunctor(f) < indx) {
+	Yap_ArithError(TYPE_ERROR_EVALUABLE, t1, "X is Y^[A]");
+	return FALSE;      
+      }
+    }
+    t1 = ArgOfTerm(indx, t1);
+    t2 = TailOfTerm(t2);
+  }
+  if (t2 != TermNil) {
+    Yap_ArithError(TYPE_ERROR_EVALUABLE, t2, "X is Y^[A]");
+    return FALSE;
+  }
+  return Eval(t1 PASS_REGS);
+}
 
 static Term
 Eval(Term t USES_REGS)
@@ -77,6 +124,12 @@ Eval(Term t USES_REGS)
 			      "functor %s/%d for arithmetic expression",
 			      RepAtom(name)->StrOfAE,n);
       }
+      if (p->FOfEE == op_power && p->ArityOfEE == 2) {
+	t2 = ArgOfTerm(2, t);
+	if (IsPairTerm(t2)) {
+	  return get_matrix_element(ArgOfTerm(1, t), t2 PASS_REGS);
+	}
+      }
       *RepAppl(t) = (CELL)AtomFoundVar;
       t1 = Eval(ArgOfTerm(1,t) PASS_REGS);
       if (t1 == 0L) {

H/iatoms.h

@@ -150,6 +150,7 @@
   AtomLT = Yap_LookupAtom("<");
   AtomLastExecuteWithin = Yap_FullLookupAtom("$last_execute_within");
   AtomLeash = Yap_FullLookupAtom("$leash");
+  AtomLength = Yap_FullLookupAtom("length");
   AtomList = Yap_LookupAtom("list");
   AtomLive = Yap_FullLookupAtom("$live");
   AtomLoadAnswers = Yap_LookupAtom("load_answers");

H/ratoms.h

@@ -150,6 +150,7 @@
   AtomLT = AtomAdjust(AtomLT);
   AtomLastExecuteWithin = AtomAdjust(AtomLastExecuteWithin);
   AtomLeash = AtomAdjust(AtomLeash);
+  AtomLength = AtomAdjust(AtomLength);
   AtomList = AtomAdjust(AtomList);
   AtomLive = AtomAdjust(AtomLive);
   AtomLoadAnswers = AtomAdjust(AtomLoadAnswers);

H/tatoms.h

@@ -298,6 +298,8 @@
 #define AtomLastExecuteWithin Yap_heap_regs->AtomLastExecuteWithin_
   Atom AtomLeash_;
 #define AtomLeash Yap_heap_regs->AtomLeash_
+  Atom AtomLength_;
+#define AtomLength Yap_heap_regs->AtomLength_
   Atom AtomList_;
 #define AtomList Yap_heap_regs->AtomList_
   Atom AtomLive_;

misc/ATOMS

@@ -155,6 +155,7 @@ A	LOOP			N	"_LOOP_"
 A	LT			N	"<"
 A	LastExecuteWithin	F	"$last_execute_within"
 A	Leash			F	"$leash"
+A	Length			F	"length"
 A	List			N	"list"
 A	Live			F	"$live"
 A	LoadAnswers		N	"load_answers"