John Baker wrote, in the JOD encoding thread:
> I just a quite look at the ascii85 verbs.
ASCII85 provides an example of J's stark beauty:
ascii85 =: (33 + 85 #.^:_1: 256 #. _4 ]\ ])&.(a.&i.)
The example would be even more compelling if it were invertible. At present,
this formulation is not, for two reasons:
(1) f^:_1: NB. note the trailing colon
is not invertible, and probably never
will be:
http://www.jsoftware.com/jwiki/System/Interpreter/Requests07#head-a937314ba3404f971e079b5d77269131de4ca9ab
(2) x&(#.^:_1) NB. as opposed to (x&#.)^:_1
is not invertible, though someday it
might be:
http://www.jsoftware.com/jwiki/System/Interpreter/Requests#head-6dfc48377d34ebb2235f3c1874230ab35ead51bf
To work around these limitations, we can express the transformation differently:
ascii85 =: (33 + [: (85&#.^:_1) 256 #. _4 ]\ ])&.(a.&i.)
which is not so bad, I suppose. Only 5 characters/4 words longer. Though the
cap and the extra nesting irk me.
Of course, for real-world applications, it is better to use the definitions in
~addons\convert\misc\ascii85.ijs .
-Dan
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