Closures

In Aqua, you can create an arrow within the function, enclosing its context.
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service Hello:
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  say_hello(to_name: string, peer: string)
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​
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func bar(callback: string -> ()):
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   callback("Fish")
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​
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func foo(peer: string):
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  on peer:
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    -- Capture service resolution
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    Hello "world"
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    -- Create a closure named "closure"
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    closure = (name: string) -> string:
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      -- Use a value that's available on the definition site
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      -- To call a service that's resolved on the definition site
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      Hello.say_hello(name, peer)
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      -- Return a value from the closure; syntax is the same as in functions
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      <- name
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  -- Pass this closure to another function
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  bar(closure)
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Closures can be created anywhere in the function, starting with Aqua 0.4.1, and then used just like any other arrow (argument of arrow type, function, or service method): passed to another function as an argument, or called right there.
Closures enclose over three domains:
Values in scope,
Service resolutions,
Topology: place where the closure is defined should be the place where it's executed.
Comparing with functions, closures have one important difference: functions are detached from topology by default. func keyword can be used to bring this behavior to closures, if needed.
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service Hello:
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  say_hello()
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​
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func foo():
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  on HOST_PEER_ID:
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    Hello "hello"
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    -- This closure will execute on HOST_PEER_ID
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    closure = () -> ():
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      Hello.say_hello() 
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    fn = func () -> ():
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      Hello.say_hello()
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  -- Will go to HOST_PEER_ID, where Hello service is resolved, and call say_hello     
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  closure()        
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  -- Will be called on current peer, probably INIT_PEER_ID, and may fail
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  -- in case Hello service is not defined or has another ID
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  fn()
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It is not yet possible to return an arrow from an arrow.

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Imports And Exports

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