Tcl was not originally intended to be used for writing large programs on its own, but to act as an interface to compiled programs. The actual heavy lifting was

Tcl was not originally intended to be used for writing large programs on its own, but to act as an interface to compiled programs. The actual heavy lifting was meant to be done in C, while interactions with the user could be quickly prototyped in Tcl. Tk simply added a way to do this graphically. The name 'Tool Control Language' points at its intended niche.