Category:Factor-numspec: Difference between revisions

{{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 creates a lazy list of integers. Whether the list ends or not depends on whether you end the specification with <code>...</code> or not.

Get all three-digit numbers beginning and ending with <code>3</code>:

<lang factor>USING: lists numspec prettyprint ;

NUMSPEC: 3_3 ;

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 ;

NUMSPEC: 3 33 3_3 ;

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 ;

NUMSPEC: 3 33 3_3 ... ;

[ 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>).

<code>numspec</code> comes with symbols for common digit restrictions. Let's get a list of the numbers with prime digits.

<lang factor>USING: lists lists.lazy numspec prettyprint ;

20 NUMSPEC: P PP ... ; 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>

Adding your own digit restrictions is easy. Just define a 1-character constant as a list with the possibilities.

<lang factor>USING: lists lists.lazy numspec prettyprint ;

CONSTANT: V L{ 2 5 }

NUMSPEC: 9 99 9V9 ... ;

30 swap 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>