Practical Programming in Tcl and Tk, Fourth Edition

Chapter 6. Control Structure Commands

This chapter describes the Tcl commands that implement control structures: if, switch, foreach, while, for, break, continue, catch, error, and return.

Control structure in Tcl is achieved with commands, just like everything else. There are looping commands: while, foreach, and for. There are conditional commands: if and switch. There is an error handling command: catch. Finally, there are some commands to fine-tune control structures: break, continue, return, and error.

A control structure command often has a command body that is executed later, either conditionally or in a loop. In this case, it is important to group the command body with curly braces to avoid substitutions at the time the control structure ...