Some lambdas

lala.py

# Author: David Beazley (https://www.dabeaz.com)
# Twitter: @dabeaz

from functools import reduce
run = lambda s: reduce(lambda *_:..., iter(lambda s=[s]:
                      (_:=s.pop()(),s.append(_))[0], None))

const   = lambda v,c   : lambda: c(v)
add     = lambda x,y,c : lambda: c(x+y)
mul     = lambda x,y,c : lambda: c(x*y)
gt      = lambda x,y,c : lambda: c(x>y)
display = lambda v,c   : lambda: (print(v), c)[1]
cbranch = lambda t,c,a : (a,c)[bool(t)]
branch  = lambda c     : c
ret     = lambda c,r   : lambda: c(r)
halt    = lambda *_    : None
_       = lambda *t    : lambda: t[0]()

fact = lambda n, c: _(
    init:= _(
        const (1, lambda r0:
        const (1, lambda r1:
        branch (loop(r0, r1))))
    ),
    loop:= lambda x, result: _(
        gt  (x, n, lambda r2:
        cbranch (r2, exit, body)),

        body:= _(
            mul (x, result, lambda r3:
            const (1, lambda r4:
            add (x, r4, lambda r5:
            branch (loop(r5, r3)))))
        ),
        exit:= _(
            ret (c, result),
        ),
    )
)

run(const (5, lambda r1:
    fact (r1, lambda r2:
    display (r2,
    halt))))

print_n_fact = lambda n, c: _(
    init:= _(
        const (1, lambda r0:
        branch (loop(r0)))
    ),
    loop:= lambda x: _(
        gt (x, n, lambda r1:
        cbranch (r1, exit, body)),

        body := _(
            fact (x, lambda r2:
            display (r2, lambda:
            const (1, lambda r3:
            add (x, r3, lambda r4:
            branch (loop(r4))))))
        )
    ),
    exit:= _(
        ret (c, None)
    )
)

run(const (10, lambda r1:
    print_n_fact (r1,
    halt)))