Re: Is multi-level function return possible?

George Neuner <gneuner2@comcast.net> writes:
>YMMV, but ISTM that recursion is not really relevant to the issue:
>lexical scoping by itself introduces the potential for name shadowing
>and the rule always has been to reference the instance which is
>defined "closest" to the point of use. The addition of recursion
>simply makes locating that closest instance - at least in part - a
>runtime operation rather than a compile time operation.


Take a look at the example from Bakul Shah in
http://compilers.iecc.com/comparch/article/14-03-042. There the "goto
lab1" skips one invocation of top to jump into a top frame that is
further out. There is no more run-time operation necessary than
without recursion: the goto just follows the static link chain for as
many levels as are lexically between the goto and the target label (in
this case one), that's all.


>Standard Pascal did have not have closures: you could pass a function
>by name as an argument to another, but its definition had to be
>visible both at the point of passing the name and at the point of
>invocation [through the aliasing argument].


Not sure what you mean with "the aliasing argument", but the original
name need not be visible at the point of invocation. Pascal's
function/procedure arguments have many properties of full closures, in
particular access to variables of enclosing scopes, but unlike
first-class closures, you could not store them into variables or pass
them out from functions.


Language design note: Given that nested functions have fallen out of
favour in the Algol-family world (in C and its offspring), I wonder if
they only really gain usefulness when combined with first-class
closures.


- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

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