Higher-order functions: Difference between revisions

First define the higher order functions <code>map</code>, <code>filter</code>, and <code>fold</code>.

<pre> [ stack ] is map.act ( --> s )

protect map.act

[ map.act put

[] swap witheach

[ map.act share do

nested join ]

map.act release ] is map ( [ x --> [ )

[ stack ] is filter.act ( --> s )

protect filter.act

[ filter.act put

[] swap witheach

[ dup

filter.act share do

iff [ nested join ]

else drop ]

filter.act release ] is filter ( [ x --> [ )

[ stack ] is fold.act ( --> s )

fold.act release ] is fold ( [ x --> x )</pre>

Then test them in the Quackery shell by reversing every string in a nest of strings, removing all the negative numbers from a nest of numbers, and flattening a deeply nested nest.

<pre>/O> $ "esreveR yreve gnirts ni a tsen fo .sgnirts" nest$

Stack empty.

/O> ' [ 1 2 [ [ 3 4 ] ] 5 [ 6 [ 7 [ 8 [ 9 ] ] ] ] ]

... [ dup

... ' join fold

... tuck = until ]

... echo

...

[ 1 2 3 4 5 6 7 8 9 ]

Stack empty.

</pre>