everything has a string rep available. It used to be that every thing was also represented literally by a string. So, for pedagogical purposes, a value 1 would be "1", and to do math, Tcl would do a strtol(val_storage), with the obvious performance implications.

The way things are done now (and have been for a long time), is that values are stored in a

    struct Tcl_Obj{
      int refCount; // objs can be shared
      int myType; // indicates whether currently a long, double, etc
      long longVal;
      double dblVal;
      [...]
      char *stringRep;
      int len;
    }

...in fact, the Tcl_Obj is more sophisticated than this, but for demonstration purposes this is fine.

So "native" (eg: longVal) values are used when appropriate, no marshalling back/forth between strings, but the string rep is always available (can be generated), because that's what Tcl promises: everything is representable as a string. This is what brings the homoiconicity to Tcl - logically it's just passing text tokens around, and emitting text tokens. Internally, again, more sophisticated, but you get the point.