ArneBab, (edited ) German 
define-typed: a static type syntax-rules macro for #Guile to create API contracts and help the JIT compiler create more optimized code:
https://www.draketo.de/software/guile-snippets#define-typed
Improved thanks to feedback from Vivien and Zelphir in the Guile User mailing list.
Just 26 lines to get argument and return value typing without changing Guile.
I love the flexibility of #Scheme ❤️
