A Lisp for V, with tail calls that are actually free
A small Lisp dialect built on an explicit CEK machine. Tail calls reuse their frame instead of pushing one, so a loop is a loop and not a stack that grows until it dies.
A taste
(define (fib n)
(if (< n 2)
n
(+ (fib (- n 1))
(fib (- n 2)))))
(fib 20) ;=> 6765What it is
Real tail calls
A quarter of a million iterations end with an empty continuation stack. Mutual recursion tail-calls too, which is the part most trampolines skip.
An explicit machine
Evaluation is a data structure you can inspect, not a recursive function you have to trust. Every step is counted, and every limit is a field you can set.
Embeddable by shape
The machine is a library with no global state. print output is collected into a field, so a host can capture it rather than fight it.
Where it stands
Working: the reader, closures, arithmetic, branching, loop, dotimes, letrec, cond, case, and proper tail calls including mutual recursion.
Not yet: let*, rest parameters, callable keywords, modules, and macros. Each one is named in the repository rather than quietly missing.