Hi,
I have added my first shot at recursive lambdas. SVN 153.
/// Jürgen
On 03/03/2014 02:01 PM, Elias Mårtenson wrote:
I would like to suggest that the most convincing example is that of
consistency. If { } can be used to wrap arbitrary APL code in an
anonymous function, then it makes sense that you can also nest them.
I'd also like to present my previous email as an example to a
situation where I wanted nested lambdas.
Regards,
Elias
On 3 March 2014 20:13, Juergen Sauermann
<[email protected] <mailto:[email protected]>>
wrote:
Hello Daniel,
I would like to explain my point of view regarding Lambdas aka.
D-funs.
Initially I considered them as not needed; they are not defined in
the APL
standard and the rules related to them seem to be rather unclear.
After seeing some requests to support them I started thinking
about this
and I figured that they could be somewhat elegant in particular when
used with the EACH operator.
There are still things related to lambdas that I don't like at all
because I
believe that they obscure the APL language more than they help.
For example, IMHO the following is definitely unfortunate (even though
possibly convenient and supported in some APL interpreters):
- having different binding rules in lambdas than in normal APL
functions,
- "guards" like :IF in lambdas
- probably more...
Nested lambdas are sort of on the border - I could look into this
if you
have a convincing example. A good specification of lambdas would
also help.
In the meantime you can work around this by eg:
A←{⍵} ◊ {⍵+A 1}1
In GNU APL lambdas create normal user-defined functions and
normally follow
their rules. That's why x becomes visible in your example, and
IMHO this makes
more sense than hiding x in lambdas but not in user-defined functions.
/// Jürgen
On 03/02/2014 11:53 AM, Daniel H. Leidisch wrote:
Hello!
Bindings from inside d-fns/lambdas leak into the global
environment:
x
VALUE ERROR
x
^
{x←⍵}1
1
x
1
I didn't read much about this, but as far as I understand,
bindings
introduced in these functions are supposed to be lexical
locals. Anyway,
this doesn't happen in NARS2000, Dyalog and NGN.
Regards,
On 03/02/2014 11:56 AM, Daniel H. Leidisch wrote:
Hello!
Nesting d-fns doesn't seem to work:
{⍵+{⍵}1}1
DEFN ERROR
This works in NARS2000, NGN and Daylog. I'm at r148.
Regards,
Daniel
