Actually my quest is to write the FFT code at the lambda-calculus level. Why? First for the fun and also because I consider that lambda-calculus is for the mind what assembly language is for the computer. See http://lambdaway.free.fr/lambdaspeech/?view=PLR. In this page I would like to replace the inefficient unary numeration by a more efficient decimal position numeration and I guess that FFT, the Katsuba or any divide & conquer algorithm could be useful. It should be pleasant for the mind and could overcome limits of the JS numbers implementation.