>>>>> "Scott" == Scott Brown <[email protected]> writes:
Scott> I have started learning Factor and after trying out the
Scott> palindrome tutorial, I am now trying to make a simple program for
Scott> filtering out non-prime numbers from a list.
Scott> I have made a word multiple-of? which returns true if x is a
Scott> multiple of y.
Scott> : multiple-of? ( x y -- ? ) [ = not ] [ mod 0 = ] 2bi and ;
Scott> I would like to use it filter a sequence of numbers like the
Scott> expression below, but looping through each of the numbers in the
Scott> sequence to remove its multiples, leaving only prime numbers.
Scott> { 2 3 4 5 6 7 8 9 10 } [ 2 multiple-of? not ] filter
Scott> Is there some loop or combinator that I could use to do this in
Scott> Factor?
You can apply the filtering process with every number instead of just
2 by using `curry'. This word lets you "insert" an element into a
quotation.
For example,
2 [ multiple-of? not ] curry
is equivalent to
[ 2 multiple-of? not ]
This way, you can build the quotation to give to filter for every number
in the list by iterating with "each":
{ 2 3 4 5 6 7 8 9 10 } dup [ [ multiple-of? not ] curry filter ] each
You can check that it works as expected by using a longer list, from 2
to 50 for example:
USE: math.ranges
2 50 [a,b] dup [ [ multiple-of? not ] curry filter ] each
=> V{ 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 }
As a side note, you can obtain prime numbers more easily:
USE: math.primes
50 primes-upto
=> V{ 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 }
Sam
--
Samuel Tardieu -- [email protected] -- http://www.rfc1149.net/
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