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Possible bracket mismatch in documentation?
It seems like (handler{ fun emit(msg){ println(msg) })( fn(){ hello() } ) in section 3.1.5 don't have correct pairs of bracket which is very confusing.
Another possible bracket mismatch is finally(fn(){ println... }), fn(){ println("entering"); throw("oops") + 42 })
Ouch, confusing indeed! Thanks for finding this -- I'll fix it :-) Changed to:
-
(handler{ fun emit(msg){ println(msg) } })( fn(){ hello() } ) -
finally(fn(){ println(...) }, fn(){ println("entering"); throw("oops") + 42 })
Any suggestions for documentation improvement is welcome -- always tricky to write in a way that strikes the right balance between explaining from first principles and staying interesting enough :-)
If handler desugar like that, then when with keyword desugar to f(e1,...,eN, fn(){ <body> }), wouldn't it be handler(fun () { fun emit(msg){ println(msg) } }, fun(){ hello() });? What's stuff handler will return? The document didn't explain about that much.
Ah good remark! I had to think twice when I saw your response :-)
handler{ <ops } is a syntactical construct and not a function handler applied to a function block { <ops> } (which makes sense as the <ops> bind the operations and are complex syntactical constructs themselves, much like a match(<expr>){ <cases> } expresssion).
So the expression handler{ <ops> } evaluates to a function with type ( action : () -> <l | e> a ) -> e a for an effect l.
And the desugaring of with handler { <ops> }; action() is thus with (handler{ <ops> }); action() is (handler{<ops>})(fn(){action()})
Hope this helps, I will try to clarify the docs.
(and I agree it is a bit inconsistent: normally braces are just for function blocks but not with match, handler, and within struct /con definitions.)