That is indeed what is being done. Except its done in one line. The 2 is inferred from the count of names in 'a b', 'a b' are provided with default values (if they are passed nulls) all in that same line, and so there is no minimum required parameters to pass, and so the assert isn't necessary.
----- Original Message ----- From: Raul Miller <[email protected]> To: Programming forum <[email protected]> Cc: Sent: Monday, June 22, 2015 2:11 PM Subject: Re: [Jprogramming] varargs and a way to manipulate local assignments Here's an example of how I think I'd do a varargs in J: example=:3 :0 assert. 2<:#y 'a b'=.2 {.y rest=.2}.y ... That said, it's quite often better to rewrite modules from first principles and/or the underlying requirements. -- Raul On Mon, Jun 22, 2015 at 1:54 PM, 'Pascal Jasmin' via Programming <[email protected]> wrote: > Finally found a clean way to manipulate local assignments. > > First, I posted before how to manipulate default function parameters > > dflt =: ([`]@.(0 = #@>@[)"0 0) (1 : (':'; '(linearize (#y) {. x) u > y'))&(<^:(L. = 0:)) > > it replaces null parameters with a default value > > (11;a:) dflt 3;4 > ┌──┬─┐ > │11│4│ > └──┴─┘ > > > but it also cuts off input to be limited to the number of default parameters > (often a good thing) > > (11;2;3) dflt 3 ; a: > ┌──┬─┐ > │11│2│ > └──┴─┘ > > > varargs is a concept in many dynamic languages which allows a function > signature to capture all of the leftover function parameters into an array. > > lr =: 3 : '5!:5 < ''y''' > ql =: 2 : '(quote m) , n' > > varargs1 =: 1 : '(m ql '' =. '' , lr@:dflt) ; [ }.~ #@]' > do0ret1 =: [: empty^:(('<0$a:' -: lr@:{.) *. 1 = #) }. [ [: ". 0&{:: > varargs =: 1 : '[: do0ret1 m varargs1' > > the m parameter to the varargs adverb is the local names to assign to the > "fixed" default parameters. After assigning, it returns the left over params. > > as a test function: > > > tonull =: NULL"_^:(0 = #) > tvarargs =: 3 : 'a + b * +/ tonull > rest =. (y ''a b'' varargs 3;4) ' > > +/ i.0 NB. reason for tonull > 0 > NULL -: +/i. 0 0 > 1 > > > tvarargs 3;a: > 3 > tvarargs a: > 3 > > tvarargs a:,7;2;3;1 > 45 > 3 + 7 * +/ 1 2 3 > > tvarargs 4 5 ;3 2; <"1 i.4 2 > 40 37 > > can also be used with tacit code, but needs a "late binder" > > lval_z_ =: 1 : 0 > 3 : m @] > ) > > ('a'lval + 'b'lval * [: +/@:tonull@:> (3;4) 'a b' varargs~ ]) a:,a:, <"1 i.4 2 > 51 67 > an explicit function that uses a more complex conversion for null 2nd > parameter > > tvarargs2 =: 3 : 0 > rest =. +/ tonull > y 'a b' varargs 3;a: > b =. (a + rest)"_^:(0 = #) b > a + b * rest > ) > (basically first line leaves b null if null is passed to it) > > tvarargs2 a: > 3 > tvarargs2 13;a: > 13 > tvarargs2 13;a:,2;3 > 103 > > 13 + 18 * +/ 2 3 > 103 > ---------------------------------------------------------------------- > 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
