YR Chen wrote:
> Ok, I'm really confused about the exact semantics of this new syntax.
> Can you give explicit rules? As far as I can tell, this "sugar function"
> can either desugar to a (const declaration + assignment + function call
> + anonymous function) or just (function call + anonymous function), and
> I'm not sure whether a specific sugar function usage desugars to the
> former or the latter.
First, to give a simple rule, you can use these keywords just like
the |function| keyword. Similar syntax forms have similar meanings.
For example:
use sugar Class;
...
function Point (...) {...}
Class Point (...) {...}
Here we have a Class declaration that looks just like a function
declaration -- it's in a statement position, not in an expression,
and there's a name before the "(". When a sugar keyword is used in
this way it binds the newly created function/class/constructor/etc
to the name.
Desugaring the above:
const Point = Class (function Point (...) {...});
However:
Pt = function Point (...) {...}
Pt = Class Point (...) {...}
Pt = function (...) {...}
Pt = Class (...) {...}
Here we use the keyword in an expression, so that it returns the
newly created function/class/constructor/etc. Then if we write a
name before the "(" it's only internal.
Desugaring the above, in order:
Pt = Class (function Point (...) {...});
Pt = Class (function (...) {...});
However, just like any other function, a sugar keyword can have
very different meanings, depending on what the sugar-function
code does. Depending on the meaning, some of the above forms
may not make sense for a given keyword.
There's also a form that is not allowed with the |function| keyword
but can make perfect sense for a given sugar keyword. You can use
it in a statement position without a name before the "(":
use sugar until;
...
until (x > 42)
{ ++x;
}
The simplified desugaring that I showed in the thread starter can't
implement the above functionality. A more complete desugaring would be:
until
( function() {return x > 42},
function()
{ ++x;
}
);
(But this is still simplified. For more, see other post.)
--
Ingvar von Schoultz
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