I first encountered lambdas in the mid-70s, and I have thought about them a lot and taken a number of classes which use them. For that matter, I have implemented the Y combinator in J (or, at least, something that works the same way).
With that in mind, I am curious: what do you mean by "a nice lambda syntax"? Thanks, -- Raul On Tue, Jan 27, 2015 at 1:24 PM, Tobia Conforto <[email protected]> wrote: > I, for one, found Raul's solution an interesting challenge to decode by > myself, purposely not looking at his explanation until I had cracked it > myself. > > Coming from a traditional and functional programming background, with some > recent APL study, I find explicit definitions much easier to understand > than J's verb trains. I still don't understand the philosophical reason why > J won't have a nice lambda syntax, analogous to {…} in modern APL or the > countless variations of (lambda …) or function() {…} in other languages. > > It would make it easier to nest function definitions, avoid unnecessary > string escaping, and introduce nested local (lexical) scoping, something > that seems conspicuously missing in J to my novice eyes. I'm sure there is > a reason, but I cannot see it yet. I get that { and } were too valuable as > standalone characters, but then I'm sure the authors could have found a > different pair of balanced symbols to use for this purpose, if they wanted. > > > On Tue, Jan 27, 2015 at 3:43 PM, Raul Miller <[email protected]> wrote: > >> Are you asking for this? >> >> f=:13 :'y </.~ +/\ t * _1 |. t=. y ~: {.;:''&''' >> >> Thanks, >> >> -- >> Raul >> >> On Tue, Jan 27, 2015 at 4:22 AM, Linda Alvord <[email protected]> >> wrote: >> > >> > >> > Here's a challenge: >> > >> > >> > >> > Just because @ might show up in third grade, that doesn't include all its >> > little cousins like @: & and &: >> > >> > >> > >> > To me, minimal documentation begins with the data using capital letters >> for >> > the name. Since F is not a verb, don't start here. >> > >> > >> > >> > F=: </.~ +/\@(-.@+._1&|.)@:=&(<,'&') >> > >> > >> > >> > Also it is a very tangled verb: >> > >> > 5!:4 <'F' >> > >> > -- ~ --- /. ---- < >> > │ -- \ --- / --- + >> > │ │ >> > │ │ -- -. >> > --+ -- @ -+ -- @ -+- +. >> > │ │ │ │ >> > │ -- @: --+ L-----+ -- _1 >> > │ │ │ L- & -+- |. >> > L- & -+ L- = >> > >> > >> > >> > Begin here with the data: >> > >> > L- <,'&' >> > >> > ]T=: ;:'4&count int 3 8&inrange' >> > >> > --T-T-----T---T---T-T-------┐ >> > │4│&│count│int│3 8│&│inrange│ >> > L-+-+-----+---+---+-+-------- >> > >> > >> > >> > Here's the challenge. Just for fun, write a single line direct >> definition of >> > F. Use simple J. You may use @ and name the verb f. >> > >> > >> > >> > >> > >> > f=: 13 :' (direcct defn) ' >> > >> > f T >> > >> > ------------T-----T---------------┐ >> > │--T-T-----┐│----┐│----T-T-------┐│ >> > ││4│&│count│││int│││3 8│&│inrange││ >> > │L-+-+------│L----│L---+-+--------│ >> > L-----------+-----+---------------- >> > >> > >> > >> > Apply f to T to get the result. >> > >> > >> > >> > That is usually enough information for sending a question to the forum. >> > Advanced programmers could use tacit verbs like Pascal's verb. Often you >> can >> > only explain these parts in words. Having a sample of your data and an >> > indication of whether you are planning one or two arguments for your verb >> > will help. >> > >> > >> > >> > Linda >> > >> > >> > >> > >> > >> > >> > >> > Message----- >> > From: [email protected] >> > [mailto:[email protected]] On Behalf Of Cliff >> Reiter >> > Sent: Monday, January 26, 2015 3:46 AM >> > To: [email protected] >> > Subject: Re: [Jprogramming] A parsing challenge >> > >> > >> > >> > Lovely. Tiny remark: >> > >> > >> > >> > <mailto:-.@> -.@+. could be replaced by +: >> > >> > >> > >> > On 1/26/2015 1:00 AM, Raul Miller wrote: >> > >> >> A note of explanation... >> > >> >> >> > >> >> (I have been noticing that far too much software is poorly documented. >> > >> >> And while I cannot do an adequate job of documenting other people's >> > >> >> software, I can document software I write.) >> > >> >> >> > >> >> F=: </.~ +/\@( <mailto:-.@+._1&;|.)@:=&(%3c,'&')> >> > -.@+._1&|.)@:=&(<,'&') >> > >> >> T=: ;:'4&count int 3 8&inrange' >> > >> >> >> > >> >> The first thing I do is find out where & appears: >> > >> >> =&(<,'&') T >> > >> >> 0 1 0 0 0 1 0 >> > >> >> >> > >> >> The second thing I do is rotate to the right and combine: >> > >> >> (+. _1&|.) =&(<,'&') T >> > >> >> 0 1 1 0 0 1 1 >> > >> >> >> > >> >> Except I want to mark the beginning of each section with a 1, and >> > >> >> right now they are zeros. >> > >> >> ( <mailto:-.@> -.@+. _1&|.) =&(<,'&') T >> > >> >> 1 0 0 1 1 0 0 >> > >> >> >> > >> >> As an aside, note that I could have cut that step out if I had started >> > >> >> by identifying where & does not appear (and then combine using logical >> > >> >> and instead of logical or): >> > >> >> >> > >> >> (* _1&|.) ~:&(<,'&') T >> > >> >> 1 0 0 1 1 0 0 >> > >> >> >> > >> >> Next, I use plus scan to turn my markers into keys: >> > >> >> >> > >> >> +/\ (* _1&|.) ~:&(<,'&') T >> > >> >> 1 1 1 2 3 3 3 >> > >> >> >> > >> >> Finally, I use these keys to group the original elements: >> > >> >> >> > >> >> T </.~ +/\ (* _1&|.) ~:&(<,'&') T >> > >> >> +-----------+-----+---------------+ >> > >> >> |+-+-+-----+|+---+|+---+-+-------+| >> > >> >> ||4|&|count|||int|||3 8|&|inrange|| >> > >> >> |+-+-+-----+|+---+|+---+-+-------+| >> > >> >> +-----------+-----+---------------+ >> > >> >> >> > >> >> And that exposition pretty much follows the thought process I >> > >> >> originally used to compose the sentence. >> > >> >> >> > >> >> Thanks, >> > >> >> >> > >> > >> > >> > ---------------------------------------------------------------------- >> > >> > For information about J forums see <http://www.jsoftware.com/forums.htm >> > >> > http://www.jsoftware.com/forums.htm >> > >> > ---------------------------------------------------------------------- >> > For information about J forums see http://www.jsoftware.com/forums.htm >> ---------------------------------------------------------------------- >> For information about J forums see http://www.jsoftware.com/forums.htm >> > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
