I've taken a look at the syntax for lambda in other C-like languages.
This is from Functional Java:
http://functionaljava.org/examples#Array.filter
In Functional Java you can write this D syntax:
(int i, int j) { return i % 3 == j; }
as:
{ int i, int j => i % 3 == j }
It's shorter and less cluttered/noisy than the D syntax, and it doesn't require
more type inferencing (but I think you can't put statements there, so it's less
powerful).
With that Java syntax extension you can write:
final Array<Integer> a = array(97, 44, 67, 3, 22, 90, 1, 77, 98, 1078, 6, 64,
6, 79, 42);
final Array<Integer> b = a.filter({int i => i % 2 == 0});
In D (with dlibs) it is:
auto a = [97, 44, 67, 3, 22, 90, 1, 77, 98, 1078, 6, 64, 6, 79, 42];
auto b = a.filter((int i){return !(i % 2);});
With std.algorithm it may be a bit shorter.
In Python:
a = [97, 44, 67, 3, 22, 90, 1, 77, 98, 1078, 6, 64, 6, 79, 42]
b = [x for x in a if not(i % 2)]
C#2 has lambdas, and C#3 adds closures and more type inferencing, so C#3+
supports the following syntaxes:
(int i) => { return i % 3 == 1; } // C#2
i => i % 3 == 1 // C#3
i => { return i % 3 == 1; } // C#3, with statements too
To define a delegate o delegate closure:
Func<int> foo = i => { return i % 3 == 1; };
Func<int> foo = i => i % 3 == 1;
Func<int> bar = () => 2;
But this isn't allowed:
Func<void> bar = () => 2;
Few comments I have copied relative to C#3:
>C# it automatically generates either an anonymous class or an anonymous method
>for the closure depending on if the function needs to close over the local
>scope or not.<
>When such an expression is evaluated, it produces a function-object which can
>be called with the arguments implied by the LambdaList, and whose body
>expressions have access to all the lexical variables that are visible at that
>point. The ones that are outside of the expression, whose bindings were
>established before it was created, are captured. This is why the resulting
>object is called a LexicalClosure.<
>Even when the code uses the closure more than once, the compiler creates only
>one instance of the closure. That environment is reused each time.<
Bye,
bearophile
