* make '' applicable to arrays, too, i.e. save input type
* utf8
* regex substitution
* asm-based regex engine
* [,] must be escapable in regex
* txt .consume .u sollte nicht negative Zahlen liefern
  * evtl. BigNums bauen und die Int-Funktionen entsprechend machen
* trigonometrics

* testsuite (incl. coverage test)

* consider polymorphic call-site caches instead of deffs_t_ / deffs?

* eliminate all FIXMEs
* stack underflow protection
* input prompt
* better interactive error handling when interpreting from stdin
* document ALL THE LIBRARIES
* consider https://en.wikipedia.org/wiki/Hindley%E2%80%93Milner_type_system and finally make the stuff typed correctly