swig/SWIG/Lib/tcl/tclinterp.i

/*

Tcl_Interp *interp

      Passes the current Tcl_Interp value directly to a C function.
      This can be used to work with existing wrapper functions or
      if you just need the interp value for some reason.  When used,
      the 'interp' parameter becomes hidden in the Tcl interface--that
      is, you don't specify it explicitly. SWIG fills in its value
      automatically.
*/

%typemap(in,numinputs=0) Tcl_Interp *interp {
  $1 = interp;
}