One of the basic list-manipulation functions in the C API to the Tcl C Library. Does most of the work for both linsert and lreplace.
Documentaton at http://www.tcl.tk/man/tcl8.5/TclLib/ListObj.htm .
Prototype:
int Tcl_ListObjReplace( Tcl_Interp *interp, Tcl_Obj *listPtr, int first, int count, int objc, Tcl_Obj *const objv[] )
The *listPtr object must not be shared when calling, as this function will modify it.