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
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