String substitution language, a more general macro facility than the C preprocessor, first really publicised as the ''macro'' processor for [Ratfor] in the book Software Tools. It's a sophisticated language, but tricky to use because there's no unique substitution symbol to distinguish macros from ordinary running text.

[DKF]: It's Turing-Complete, but only really used for [autoconf] hacking now (and that's a fairly heavily modified version).
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[Category Language]