afaik, $: was never meant to be used with explicit code In NuVoc, one use with explicit code is explicitly mentioned as an exception to $:’s tacit only use:
This kind of default can also be used when the dyadic valence is defined explicitly: EDIT: there’s another line which states it more directly: 3. In no case does $: refer to a larger unit than the sentence it appears in, for example an explicit definition in which it appears. So I’d say, if you want to be explicit, be explicit. Which entails calling oneself by one’s name rather than ‘me’. Am 27.10.20 um 22:01 schrieb 'Michael Day' via Programming: > OK - not extended arithmetic... > > Having been keen on direct definition in APL for many years, I've just > started looking back at > the late John Scholes' description of his Dfns in Dyalog APL, to be > found at > https://www.dyalog.com/uploads/documents/Papers/dfns.pdf > > I tried coding a couple of simple recursive examples as DDs in J, namely > sieve (Primes) and fac(torial): > > sieve =: {{)v > '' sieve y > : > nxt =. {. y > msk =. 0~: nxt | y > if. */ }. msk do. > x, y > else. > (x,nxt) sieve msk#y > end. > }} > > fac =: {{)v > 1 fac y > : > if. y = 0 do. > x > else. > (x * y) fac y - 1 > end. > }} > > They work fine: > sieve 2}.i.21 > 2 3 5 7 11 13 17 19 > fac 8 > 40320 > > BUT - Dfns allows self-reference of anonymous functions with the delta > symbol, ∇, > which _might_ display ok here. SO, where I've got "sieve" or "fac" > within the dyadic sections of > these definitions, John had ∇ (delta). (He allowed ambivalent > functions by having an optional > default assignment of ⍺, alpha, ie x for J users.) > > However, replacing (x * y) fac y - 1 by (x * y) $: y - 1 results in, eg: > fac 8 > |stack error: fac > | (x*y) $:y-1 > > Is this my poor understanding of $: - I don't use it much - or is it > an instance of the problem with > $: that Henry noted in "Re: [Jbeta] Error with $:" on 11/Oct/20, or > something else? > > Thanks again, > > Mike > > PS - In case the APL displays reasonably well, here are copies of these > 2 Dyalog Dfns: > (The line numbers are not part of the definitions.) > Lines sieve[4] and factorial[2] are examples of "Guards" which are sort of > if. test then. value return. end. > > sieve←{ ⍝ Sieve of Eratosthenes. > [1] ⍺←⍬ ⍝ Default no primes yet.* > [2] nxt←1↑⍵ ⍝ Next prime, and > [3] msk←0≠nxt|⍵ ⍝ ... mask of non-multiples. > [4] ∧/1↓msk:⍺,⍵ ⍝ All non multiples - finished. > [5] (⍺,nxt)∇ msk/⍵ ⍝ Sieve remainder. > [6] } > > factorial←{ ⍝ Tail recursive factorial. > [1] ⍺←1 ⍝ * > [2] ⍵=0:⍺ > [3] (⍺×⍵)∇ ⍵-1 > [4] } > > * examples of default value of left argument if applied monadically. > > > -- ---------------------- mail written using NEO neo-layout.org ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
