\ Euler problem 14 in ANS Forth: 64-bit only.
: even? 2 mod 0= ;
: collatz dup even? if 2/ else 3 * 1+ then ;
: valid? 1 > ;
: collatz# 1 >r begin dup valid? while collatz r> 1+ >r repeat drop r> ;
variable largest \ ...sequence length
variable start \ ...of sequence with maximum length
: note start ! largest ! ;
: longer? largest @ > ;
: (solve) 0 do i collatz# dup longer? if i note else drop then loop ;
: solve 0 largest ! 0 start ! (solve) start @ ;
: go 1000000 solve . ;