Forced metafunction resolver to check arity on monoarity functions

src/classes/metafunction.c

@@ -1175,6 +1175,14 @@ static bool mfcompiler_emitresolver(mfcompiler *compiler, int nresolutions, mfco
         exactpath.knownarity = resolutions[0].nparams;
         exactpath.aritychecked = true;
         path = &exactpath;
+
+        // Add a sparse to verify that nargs matches the known arity
+        mfindx deflt;
+        mfcompiler_emitfail(compiler, &deflt);
+        mfcompilersparseentry correctarity;
+        correctarity.value = path->knownarity;
+        ERR_CHECK_RETURN(mfcompiler_emitresolver(compiler, nresolutions, resolutions, path, &correctarity.target));
+        return mfcompiler_emitsparse(compiler, 1, &correctarity, deflt, entry);
     }
 
     /* For exact arity without typed params, emit the lone fixed-arity winner. */
@@ -1298,7 +1306,7 @@ void metafunction_disassemble(objectmetafunction *fn) {
 static bool metafunction_runresolver(objectmetafunction *fn, int nargs, value *args, error *err, value *out) {
     mfinstruction *instructions = fn->resolver.data;
     if (!instructions) return metafunction_resolveslow(fn, nargs, args, err, out);
-    
+
     mfindx pc = fn->entry;
     int reg = nargs; // Single register initialized with nargs
 
@@ -1307,7 +1315,7 @@ static bool metafunction_runresolver(objectmetafunction *fn, int nargs, value *a
             case MFOP_SLOW:
                 return metafunction_resolveslow(fn, nargs, args, err, out);
             case MFOP_RESOLVE: {
-                pc++; *out=fn->fns.data[instructions[pc]];
+                *out=fn->fns.data[instructions[++pc]];
                 return true;
             }
             case MFOP_FAIL:

test/matrix/identity.morpho

@@ -12,4 +12,4 @@ print a
 // expect: [ 0 0 1 ]
 
 a = IdentityMatrix()
-// expect error 'MtrxIdnttyCns'
+// expect error 'MltplDsptchFld'

test/string/err_split_args2.morpho

@@ -0,0 +1,3 @@
+
+print "Hello world".split(2)
+// expect error 'MltplDsptchFld'

test/string/err_split_args3.morpho

@@ -0,0 +1,4 @@
+// You can not add extra arguments to a function
+
+print "Hello world".split(" ", 2)
+// expect error 'MltplDsptchFld'

test/string/err_split_args4.morpho

@@ -0,0 +1,5 @@
+print "Hello world".split(" ")
+// expect: [ Hello, world ]
+
+print "Hello world".split()
+// expect error 'MltplDsptchFld'