This function seems generally useful, or at least is convenient for me. Its
also an easy way to "decorate" any function to automagically deal with nil
arguments in what I think is the best generic way. It makes sense to keep this
as user code, because the "right" function is personal or situational anyway.
NB. adverb treats u as dyad. If either argument is nil, it returns the other.
If both are
NB. nil, it returns the identity function value, or nil if not defined.
smartnils =: 1 : 0 NB. assumes all 0 element arguments (0=#y) are equivalent to
nil.
if. 0=#y do. (u/ :: ]) i.0 return. end.
y
:
if. 0=#x do.
if. 0=#y do. (u/ :: ]) i.0 return. end.
y return. end.
if. 0=#y do. x return. end.
x u y
)
(1 ; '' ; 2 ; '') ( [ each + smartnils each ]) 2 ;'' ; 4 ; 5
+-+-+-+-+
|3|0|6|5|
+-+-+-+-+
(1 ; '' ; 2 ; '') ( [ each + each ]) 2 ;'' ; 4 ; 5
+-++-++
|3||6||
+-++-++
(1 ; '' ; 2 ; '') ( [ each +:@* smartnils each ]) 2 ;'' ; 4 ; 5
+-++--+-+
|4||16|5| NB. +:@*/ i.0 is undefined.
+-++--+-+
+: each (1 ; '' ; 2 ; '') ( [ each * smartnils each ]) 2 ;'' ; 4 ; 5
+-+-+--+--+
|4|2|16|10|
+-+-+--+--+
The one downside of this definition for smartnils is that 1 -: (i.0) *. i.0
but its a good template for tweaking variations that give a better answer.
----- Original Message ----
From: Pascal Jasmin <[EMAIL PROTECTED]>
To: Programming forum <[email protected]>
Sent: Sunday, October 22, 2006 5:17:55 PM
Subject: Re: [Jprogramming] Dyads and identity function
The ident adverb I was looking for would be like:
ident2 =: 1 : 0 NB. assumes all 0 element arguments (0=#y)return identity
behaviour
y
:
if. 0=#x do. y return. end.
if. 0=#y do. x return. end.
x u y
)
ident3 =: 1 : 0 NB. assumes only i.0 arguments causes identity behaviour
y
:
if. x-:i.0 do. y return. end.
if. y-:i.0 do. x return. end.
x u y
)
+ident2 33
33
(i.0) +ident2 33
33
((i.0),ident2 22) +ident2 i.0
22
$ 22 +ident3 i.0 0
0 0
incidentally, there is a bug in the documentation for identity function,
because it says that it should behave like ident2, but it really behaves like
ident3.
----- Original Message ----
From: "Miller, Raul D" <[EMAIL PROTECTED]>
To: Programming forum <[email protected]>; Programming forum
<[email protected]>
Sent: Sunday, October 22, 2006 3:09:30 PM
Subject: RE: [Jprogramming] Dyads and identity function
ident=:1 :'a:1 :(u b.1)'
For example:
+ident 99
0
+ident i. 9 9
0 0 0 0 0 0 0 0 0
--
Raul
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