first steps to implement object construction expressions

compiler/ast.nim

@@ -89,6 +89,7 @@ type
                           # formal parameters, var statements, etc.
     nkVarTuple,           # a ``var (a, b) = expr`` construct
     nkPar,                # syntactic (); may be a tuple constructor
+    nkObjConstr,          # object constructor: T(a: 1, b: 2)
     nkCurly,              # syntactic {}
     nkCurlyExpr,          # an expression like a{i}
     nkBracket,            # syntactic []