40.wsf

# Project Euler
# Problem 40: Champernowne's constant
# https://projecteuler.net/problem=40

    1 call champernowne
    10 call champernowne *
    100 call champernowne *
    1000 call champernowne *
    10000 call champernowne *
    100000 call champernowne *
    1000000 call champernowne *
    printi end

# champernowne returns the nth digit in the fractional part of the
# transcendental Champernowne's constant, that is, a fraction
# constructed through the concatenation of all positive integers:
# 0.123456789101112131415161718192021...
# (n -- digit)
champernowne:
    1 0 10
# (n exp lo hi -- digit)
.champernowne:
    ^ ^2 - ^3 * # range
    ^4 ^1 j< .champernowne_within_bounds
    ^4 swap - # n -= range
    ^3 1+     # exp++
    ^2        # lo = hi
    ^ 10*     # hi *= 10
    call .champernowne
    4slide ret
.champernowne_within_bounds:
    2drop
    ^2 ^2 / +         # num that contains digit
    swap ^2 ^1 % - 1- # index of digit
.champernowne_extract_digit:
    ^ jz .champernowne_ret
    1-
    swap 10/ swap
    jmp .champernowne_extract_digit
.champernowne_ret:
    drop 10% swap drop
    ret