# Category:Factor-numspec

**Library**

This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by 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 talk page) to a text file called `numspec.factor`

and then save it in a sub-directory called `numspec`

inside your `work`

directory. `work`

is in the same directory as the Factor executable.

Finally, in your program, make sure to add `numspec`

to your `USING:`

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 `...`

.

Get all three-digit numbers beginning and ending with `3`

:
<lang factor>USING: lists numspec prettyprint ;
DIGIT: _ 0123456789
NUMSPEC: a 3_3 ;
a list>array .</lang>

- Output:

{ 303 313 323 333 343 353 363 373 383 393 }

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>

- Output:

{ 3 33 303 313 323 333 343 353 363 373 383 393 }

But what if you don't want to make a case for every number of digits? Got you covered! `...`

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>

- Output:

{ 3 33 303 313 323 333 343 353 363 373 383 393 3003 3013 3023 }

Since this is an infinite list, we need to remember to limit it in some fashion (like with `lwhile`

).

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>

- Output:

{ 2 3 5 7 22 23 25 27 32 33 35 37 52 53 55 57 72 73 75 77 }

`2`

and `5`

surrounded by `9`

s:
<lang factor>USING: lists lists.lazy numspec prettyprint ;
DIGIT: V 25
NUMSPEC: e 9 99 9V9 ... ;
30 e ltake list>array .</lang>

- Output:

{ 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 }

## Pages in category "Factor-numspec"

The following 2 pages are in this category, out of 2 total.