the foundations of a type traits module; better error messages for expr, typedesc and typeclasses params

compiler/ast.nim

@@ -243,8 +243,13 @@ const
   sfFakeConst* = sfDeadCodeElim  # const cannot be put into a data section
   sfDispatcher* = sfDeadCodeElim # copied method symbol is the dispatcher
   sfNoInit* = sfMainModule       # don't generate code to init the variable
+
   sfImmediate* = sfDeadCodeElim  # macro or template is immediately expanded
                                  # without considering any possible overloads
+  
+  sfAnon* = sfCompilerProc  # symbol name that was generated by the compiler
+                            # the compiler will avoid printing such names 
+                            # in user messages.
 
 const
   # getting ready for the future expr/stmt merge
@@ -358,7 +363,8 @@ const
 
 type
   TMagic* = enum # symbols that require compiler magic:
-    mNone, mDefined, mDefinedInScope, mLow, mHigh, mSizeOf, mIs, mOf,
+    mNone,
+    mDefined, mDefinedInScope, mLow, mHigh, mSizeOf, mTypeTrait, mIs, mOf,
     mEcho, mShallowCopy, mSlurp,
     mParseExprToAst, mParseStmtToAst, mExpandToAst,
     mUnaryLt, mSucc,