We often say the APL family of languages allow us to use language as a tool
of thought. How does this play out in practice? Do we approach reading J
programs differently from those written in other languages? If so, how?
These questions occurred to me today while I was knocking together an
implementation of a RosettaCode task on reading configuration files. The
task is to parse file formatted like the following:
# This is the fullname parameter
FULLNAME Foo Barber
# This is a favourite fruit
FAVOURITEFRUIT banana
# This is a boolean that should be set
NEEDSPEELING
# This boolean is commented out
; SEEDSREMOVED
Fuller example at [1]. After reading the intro, I copy/pasted the example
into a J noun and proceeded to write this:
deb L:0@:(({.~ ; [: < [: ;^:(1=#) ',' cut (}.~>:)) i.&1@:e.&' =')&>@(#~
a:&~: > ';#'e.~{.&>)@:(dlb&.>)@:(LF&cut)
Which is a verb which takes the configuration text as input and produces a
table of name-value pairs as output. My first thought was "wow, I was able
to knock that together in literally less than a minute, through simple
incremental iterations in the REPL: J is AWESOME".
But then, thinking about posting it, I realized "this is awful, no one's
going to be able to read it like this, and it's going to take more work to
make it readable than it took to make it actually work".
So that got me thinking about what exactly we mean by J as a notation. And
I wondered: how could we use the language to express our thoughts more
clearly, and how does that differ from how we write J when we just want to
get something done? And is this a different or more difficult problem for
J than other languages?
So, how would you write an configuration file parser in J, if clarity were
an important concern? I'm interested in not only the actual program, but
the reasoning behind the decisions you make.
-Dan
[1] RosettaCode task to read a configuration file:
http://rosettacode.org/wiki/Read_a_configuration_file
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