Implement a concept of constant common variables (half of #46)

sorear · Nov 5, 2011 · eb2bc3c · eb2bc3c
1 parent 1491987
commit eb2bc3c
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Showing 3 changed files with 18 additions and 6 deletions.
diff --git a/lib/CodeGen.cs b/lib/CodeGen.cs
@@ -3737,7 +3737,9 @@ public class DowncallReceiver : CallReceiver {
                 if (li is LIHint) {
                     ((LIHint)li).var.v = v;
                 } else if (li is LICommon) {
-                    li.Set(null, v);
+                    StashEnt hkey = Kernel.currentGlobals[((LICommon)li).hkey];
+                    hkey.constant = true;
+                    hkey.v = v;
                 } else {
                     return new Exception("cannot bind constant value");
                 }

diff --git a/lib/Kernel.cs b/lib/Kernel.cs
@@ -326,13 +326,17 @@ public class StashEnt : IFreeze {
         public Variable v;
         public string   file;
         public int      line;
+        public bool     constant;
 
         public void Bind(Variable v) {
+            if (constant)
+                throw new NieczaException("Binding of constant common variable");
             this.v = v;
         }
 
         void IFreeze.Freeze(FreezeBuffer fb) {
             fb.Byte((byte)SerializationCode.StashEnt);
+            fb.Byte((byte)(constant ? 1 : 0));
             fb.ObjRef(v);
             fb.String(file);
             fb.Int(line);
@@ -341,6 +345,7 @@ public class StashEnt : IFreeze {
         internal static StashEnt Thaw(ThawBuffer tb) {
             StashEnt r = new StashEnt();
             tb.Register(r);
+            r.constant = tb.Byte() != 0;
             r.v = (Variable)tb.ObjRef();
             r.file = tb.String();
             r.line = tb.Int();
@@ -849,22 +854,26 @@ public sealed class RuntimeUnit : IFreeze {
             bool  nseod = nseo.IsDefined();
             bool  oseod = oseo.IsDefined();
             // lowest priority are empty common symbols
-            if (nse.v.rw && !nseod || IsEmptyAggr(nse.v)) {
+            if (nse.v.rw && !nseod || !nse.constant && IsEmptyAggr(nse.v)) {
                 nse = ose;
                 return null;
             }
-            if (ose.v.rw && !oseod || IsEmptyAggr(ose.v)) {
+            if (ose.v.rw && !oseod || !ose.constant && IsEmptyAggr(ose.v)) {
                 return null;
             }
 
             // no conflict if items are identical
-            if (ose.v == nse.v || !ose.v.rw && !nse.v.rw && oseo == nseo) {
+            if (ose.v == nse.v || !ose.v.rw && !nse.v.rw &&
+                    ose.v.islist == nse.v.islist && oseo == nseo) {
                 nse = ose;
                 return null;
             }
 
             // no conflict if items are simple packages with the same who
-            if (!ose.v.rw && !oseod && !nse.v.rw && !nseod &&
+            // note that this will effectively change a constant, but these
+            // packages are observationally identical barring &infix:<does>
+            // (mis)use
+            if (ose.constant && !oseod && nse.constant && !nseod &&
                     (oseo.mo.mo.isPackage || nseo.mo.mo.isPackage) &&
                     oseo.mo.who.Isa(Kernel.StashMO) &&
                     nseo.mo.who.Isa(Kernel.StashMO) &&
@@ -884,6 +893,7 @@ public sealed class RuntimeUnit : IFreeze {
                 string file, int line) {
             string key = (char)who.Length + who + name;
             StashEnt nse = new StashEnt();
+            nse.constant = (var != null);
             if (var == null)
                 var = MakeAppropriateVar(name);
             nse.v = var;

diff --git a/lib/Serialize.cs b/lib/Serialize.cs
@@ -64,7 +64,7 @@ struct ObjRef {
         internal static HashAlgorithm NewHash() { return new SHA256Managed(); }
 
         static readonly string signature = "Niecza-Serialized-Module";
-        static readonly int version = 4;
+        static readonly int version = 5;
 
         // Routines for use by serialization code
         public bool CheckWriteObject(SerUnit into, object o,