The long-awaited alpha release of Tcl 8.7 calls for a series of posts summarizing the enhancements in this release. The first in this series is about the new -command option to the regsub command. I have wished for this feature many times and now thanks to DKF it is now available in Tcl.

This blog post is adapted from my book The Tcl Programming Language.

What is metaprogramming? Roughly speaking, metaprogramming involves writing a program that in turn writes a program to do the desired task. In some cases metaprogramming makes for simpler or more succinct code while in others it optimizes performance by generating specialized code at runtime. Tcl lends itself naturally to this style of programming. This article illustrates one such use.