rex (programming language)
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This article is about a functional programming language used primarily by students. For the scripting language created by IBM, see REXX.
The name "rex" derives from "rewriting expressions", which is the basic principle underlying the implementation: replace an instantiation of an expression on the left-hand side of a rule with the instantiated right-hand side.
factorial(0) => 1; factorial(X) => X * factorial(X-1);