View source for Category:Factor-numspec

{{library}}
'''Factor-numspec''' is a vocabulary that aims to make tasks involving the restriction of digits within numbers easy. This vocabulary was made because there are a fair number of tasks on Rosetta Code involving this operation and more being added all the time.

To use it yourself, copy the source code (in the [http://rosettacode.org/wiki/Talk:Factor-numspec talk page]) to a text file called <code>numspec.factor</code> and then save it in a sub-directory called <code>numspec</code> inside your <code>work</code> directory. <code>work</code> is in the same directory as the Factor executable.

Finally, in your program, make sure to add <code>numspec</code> to your <code>USING:</code> like so:

<lang factor>USING: math numspec prettyprint ;</lang>

=== Examples ===
It's important to remember that a number specification defines a named lazy list constant. Whether the list ends or not depends on whether you end the specification with <code>...</code>.

Get all three-digit numbers beginning and ending with <code>3</code>:
<lang factor>USING: lists numspec prettyprint ;
DIGIT: _ 0123456789
NUMSPEC: a 3_3 ;
a list>array .</lang>
{{out}}
<pre>
{ 303 313 323 333 343 353 363 373 383 393 }
</pre>

Literals can be added where necessary. Let's make special cases for one- and two-digit numbers.
<lang factor>USING: lists numspec prettyprint ;
DIGIT: _ 0123456789
NUMSPEC: b 3 33 3_3 ;
b list>array .</lang>
{{out}}
<pre>
{ 3 33 303 313 323 333 343 353 363 373 383 393 }
</pre>

But what if you don't want to make a case for every number of digits? Got you covered! <code>...</code> rudimentarily infers the pattern.
<lang factor>USING: lists lists.lazy numspec prettyprint ;
DIGIT: _ 0123456789
NUMSPEC: c 3 33 3_3 ... ;
c [ 3030 < ] lwhile
list>array .</lang>
{{out}}
<pre>
{ 3 33 303 313 323 333 343 353 363 373 383 393 3003 3013 3023 }
</pre>
Since this is an infinite list, we need to remember to limit it in some fashion (like with <code>lwhile</code>).

Numbers with only prime digits:
<lang factor>USING: lists lists.lazy numspec prettyprint ;
DIGIT: P 2357
NUMSPEC: d P PP ... ;
20 d ltake list>array .</lang>
{{out}}
<pre>
{ 2 3 5 7 22 23 25 27 32 33 35 37 52 53 55 57 72 73 75 77 }
</pre>
<code>2</code> and <code>5</code> surrounded by <code>9</code>s:
<lang factor>USING: lists lists.lazy numspec prettyprint ;
DIGIT: V 25
NUMSPEC: e 9 99 9V9 ... ;
30 e ltake list>array .</lang>
{{out}}
<pre>
{
    9
    99
    929
    959
    9229
    9259
    9529
    9559
    92229
    92259
    92529
    92559
    95229
    95259
    95529
    95559
    922229
    922259
    922529
    922559
    925229
    925259
    925529
    925559
    952229
    952259
    952529
    952559
    955229
    955259
}
</pre>