remove try in promote part 1

Author: pzinn

M2/Macaulay2/m2/matrix.m2

@@ -75,27 +75,28 @@ reduce = (tar,rawF) -> (
 
 addHook(ReduceHooks, Strategy => Default, (tar, rawF) -> rawF % raw gb presentation tar)
 
+toSameRing = (m,n) -> (
+     R := ring m; S := ring n;
+     if R =!= S then (
+	 if isPromotable(R,S) then (promote(m,S),n)
+	 else if isPromotable(S,R) then (m,promote(n,R))
+	 else error "expected compatible rings"
+	 )
+     else (m,n))
+
 InfiniteNumber * Matrix := (r,m) -> (map(target m, source m, matrix(r*(entries m))))
 Matrix * InfiniteNumber := (m,r) -> r*m
 Number * Matrix :=
 RingElement * Matrix := (r,m) -> (
-    if ring r =!= ring m then try r = promote(r,ring m) else m = promote(m,ring r);
+    (r,m) = toSameRing(r,m);
      map(target m, source m, reduce(target m, raw r * raw m)))
 Matrix * Number :=
 Matrix * RingElement := (m,r) -> (
-    if ring r =!= ring m then try r = promote(r,ring m) else m = promote(m,ring r);
+    (r,m) = toSameRing(r,m);
      map(target m, source m, reduce(target m, raw m * raw r)))
 Matrix / Number      :=
 Matrix / RingElement := (m,r) -> m * (1/r)
 
-toSameRing = (m,n) -> (
-     if ring m =!= ring n then (
-	  try (promote(m,ring n) , n) else
-	  try (m , promote(n,ring m))
-	  else error "expected compatible rings"
-	  )
-     else (m,n))
-
 Matrix _ Sequence := RingElement => (m,ind) -> (
      if # ind === 2
      then promote(rawMatrixEntry(m.RawMatrix, ind#0, ind#1), ring m)
@@ -176,13 +177,7 @@ Matrix * Matrix := Matrix => (m,n) -> (
 	       q,
 	       Degree => degree m + if m.?RingMap then m.RingMap.cache.DegreeMap degree n else degree n))
      else (
-     	  R := ring m;
-	  S := ring target n;
-	  if R =!= S then ( -- use toSameRing?
-	       try m = promote(m,S) else
-	       try n = promote(n,R) else
-	       error "maps over incompatible rings";
-	       );
+	  (m,n) = toSameRing(m,n);
 	  M = target m;
 	  P := source m;
 	  N = source n;

M2/Macaulay2/m2/matrix1.m2

@@ -11,7 +11,7 @@ nottosamering := (X,Y) -> (
      if X === Y then error("expected ",pluralsynonym X, " for compatible rings")
      else error("expected ",X.synonym," and ",Y.synonym," for compatible rings"))
 samering = (M,N) -> if ring M === ring N then (M,N) else notsamering(class M,class N)
-tosamering := (M,N) -> if ring M === ring N then (M,N) else (
+tosamering := (M,N) -> if ring M === ring N then (M,N) else ( -- need merging with toSameRing in matrix.m2
      z := try 0_(ring M) + 0_(ring N) else nottosamering(class M,class N);
      (promote(M,ring z),promote(N,ring z)))