RE: Closures: summarizing suggestions a bit...

I think that's a good idea. It gives an easy to recognize syntactic clue as to what's going on while preserving brevity, avoiding ambiguity (for both parser and human reading the code). 

|-----Original Message-----
|From: beanshell-developers-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
|[mailto:beanshell-developers-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org]On Behalf Of
|Slava Pestov
|Sent: Thursday, February 03, 2005 4:39 PM
|To: BeanShell Developers
|Subject: Re: [Beanshell-dev] Closures: summarizing suggestions a bit...
|
|
|Hi all,
|
|I suggest a syntax for closures, somewhat inspired by Common 
|Lisp, where 
|refer to a function object, either named or anonymous, you 
|write #'foo, 
|where foo is either a function name, or an anonymous function block 
|("lambda").
|
|While #' is a bit ackward, in BeanShell you can reserve the 
|currently-unused @ character to look up inside the function 
|namespace -- 
|giving the ability to have function object literals. Using @ 
|in a C like 
|language is not that weird, and Objective C uses this character.
|
|So, suppose you had a function map() that took a list and a function, 
|and returned a new list. You could do:
|
|sq(x) { return x*x; }
|
|map(list,@sq);
|
|For anonymous closures, just use a syntax like
|
|map(list,@(x) { return x*x; });
|
|So its @(arguments) { body }
|
|(in Common Lisp, its #'(lambda (x y) (+ x y)) -- notice the 
|parallel...).
|
|Now, I missed method literals. What you could do is return an object 
|that is internally a pair; a 'this', and a BeanShell method to invoke. 
|So the syntax could be like:
|
|map(list,myObj.@foo);
|
|Where myObj.@foo is an object that when called in some way, invokes 
|myObj.foo(...).
|
|To call a method, function or closure, i think its ok to call the 'do' 
|method on it, like in SmallTalk.
|
|void map(list,closure)
|{
|     for(i = 0; i < list.size(); i++)
|         list.set(i,closure.do(list.get(i)));
|}
|
|I hope my proposal is considered. I think overloading an unused 
|punctuation character is the best way to implement anonymous closures 
|and methods-as-arguments while maintaining brevity, without creating 
|ambiguous situations.
|
|Patrick Niemeyer wrote:
|> Just to summarize a few of the alternate suggestions:
|> 
|> // Extended method-like syntax:
|> callable( ... );
|> callable( arg, ... );
|> 
|> 
|> // Anonymous inner class-like syntax:
|> () { ... }
|> (arg) { ... }
|> 
|> 
|> // Multiple curly brace syntax:
|> {{ ... }}
|> { arg { ... } }
|> 
|> 
|> 
|> Pat
|> 
|> 
|> 
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|
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