Thanks to the keyword `template', and almost by accident, C++ is a very special language where one can not only specify what a program will do once compiled, but in addition one can specify how the compiler will compile a program. This feature gave birth to powerful (albeit tricky and very error-prone) programming techniques, commonly referred to as ``metaprogramming''.
Starting from the simple idea that ``we want metaprogramming efficiency, but we don't want to write it'', e.g. in Olena (https://www.ohloh.net/p/olena) and Vaucanson (https://www.ohloh.net/p/vaucanson), the Transformers project was initiated. It aims at converting naive (but decent) C++ programming into high-speed (but indecent) C++ source code.
The software we use to build those tools comes mainly from XT.
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