A '''preprocessor''' is tool that is used to transform a program's source code before feeding it into the compiler or interpreter that implements a particular language.

Some languages ([C], [C++], [Ratfor]) are strongly dependent on their preprocessors. Tcl is not normally used that way.

** Tcl preprocessors **
   * [https://github.com/dbohdan/sqawk/blob/master/tools/assemble.tcl%|%Assemble] — Bundles multiple Tcl source code files into a single file. Understands `#define` and `#ifdef`/`#ifndef`. Assemble is developed as part of the [Sqawk] project.
   * [tpp]
   * [Tipi]

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