[REBOL] Who is that grouch? -or- Fun with functions! Re:(4)
From: joel:neely:fedex at: 5-Oct-2000 12:34
Just to bring this little exercise to closure (groan...), I'm
passing on the latest version of the functions in the post that
started this thread. Both iota and map have been modified
to take advantage of the ideas communicated/inspired by Allen's
comments. The whole thing is dramatically faster as a result.
OBTW, this thread is not really about prime numbers (even though
I've embedded this copy of map in a prime seiving object)! I've
found functions such as map highly useful in a variety of
tasks in the past, and hope it will be of some use to someone
else. It just happens that sieving for primes is a cute way
to demo what map does.
>> do %primes.r
>> length? foo: primes/sieve 1000
== 168
>> print foo
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83
89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173
179 181 191 193 197 199 211 223 227 229 233 239 241 251 257 263
269 271 277 281 283 293 307 311 313 317 331 337 347 349 353 359
367 373 379 383 389 397 401 409 419 421 431 433 439 443 449 457
461 463 467 479 487 491 499 503 509 521 523 541 547 557 563 569
571 577 587 593 599 601 607 613 617 619 631 641 643 647 653 659
661 673 677 683 691 701 709 719 727 733 739 743 751 757 761 769
773 787 797 809 811 821 823 827 829 839 853 857 859 863 877 881
883 887 907 911 919 929 937 941 947 953 967 971 977 983 991 997
-jn-
REBOL []
primes: make object! [
iota: function [n [integer!]] [r i] [
r: make block! n
repeat i n [append r i]
]
map: function [[catch] b [block!] f [function!] /all] [r v] [
r: make block! length? b
foreach c b [
if any [found? v: do [f c] all] [append/only r v]
]
r
]
nondiv: func [d] [func [n] [either n // d = 0 [none] [n]]]
square: func [n [number!]] [n * n]
sieve: function [n [integer!]] [p c d] [
p: copy []
c: next iota n
while [all [0 < length? c (square d: first c) <= last c]] [
append p d
c: map c nondiv d
]
append p c
]
]
