Numbers to words

This code defines an operator, n2w, that maps positive integers to their English equivalent.

Here is the code:

-- convert numbers to words:
-- usage: n2w |12345>
-- updated to the version 3.1.1 language


ones |1> => |one>
ones |2> => |two>
ones |3> => |three>
ones |4> => |four>
ones |5> => |five>
ones |6> => |six>
ones |7> => |seven>
ones |8> => |eight>
ones |9> => |nine>

tens |10> => |ten>
tens |11> => |eleven>
tens |12> => |twelve>
tens |13> => |thirteen>
tens |14> => |fourteen>
tens |15> => |fifteen>
tens |16> => |sixteen>
tens |17> => |seventeen>
tens |18> => |eighteen>
tens |19> => |nineteen>

ten |20> => |twenty>
ten |30> => |thirty>
ten |40> => |forty>
ten |50> => |fifty>
ten |60> => |sixty>
ten |70> => |seventy>
ten |80> => |eighty>
ten |90> => |ninety>

tens |*> #=> smerge[" "] sdrop ( ten times-by[10] int-divide-by[10] |_self> . ones mod[10] |_self> )
hundreds-rule |*> #=> smerge[" and "] (hundreds int-divide-by[100] mod[1000] |_self> . tens mod[100] |_self>)

hundreds |0> #=> |>
hundreds |*> #=> ones |_self> __ |hundred>

thousands |0> #=> |>
thousands |*> #=> hundreds-rule |_self> __ |thousand>

millions |0> #=> |>
millions |*> #=> hundreds-rule |_self> __ |million>

billions |0> #=> |>
billions |*> #=> hundreds-rule |_self> __ |billion>

trillions |0> #=> |>
trillions |*> #=> hundreds-rule |_self> __ |trillion>


op |seq> => |op: hundreds-rule> . |op: thousands> . |op: millions> . |op: billions> . |op: trillions>


-- our numbers to words operator:
n2w |0> => |zero>
n2w |*> #=> smerge[", "] sreverse op-zip(op |seq>) split-num |_self>


-- the split-number operator:
split-num |*> #=>
    if( is-less-than[1000] |__self> ):
        |__self>
    else:
        mod[1000] |__self> . split-num int-divide-by[1000] |__self>
    end:

And here are a couple of examples of n2w in action:

sa: n2w |31>
|thirty one>

sa: n2w |00037>
|thirty seven>

sa: n2w |3700>
|three thousand, seven hundred>

sa: n2w |1234567890>
|one billion, two hundred and thirty four million, five hundred and sixty seven thousand, eight hundred and ninety>

Noting that there is a limit to the size of the integers due to the back end C++.

Raw file here.