A control structure is a programming language construct which provides the coder the means to direct the flow of program execution based on some criteria.

Some examples in [Tcl] are `[if]`, `[while]`, `[for]`, `[foreach]`, and [switch] (also `[case]`, but that's obsolete).

The [Expect] extension also defines new control structures.

Tcl is also fertile ground for creating [new control structures].

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