On 26 Jun 2009, at 14:09, Timo B. Hübel wrote:
And here comes my question: If there is anybody with proper
knowledge about
this issue, I would really like to know what are those things that are
missing? For example, Clojure lacks proper tail recrusion
optimization due to
some missing functionality in the JVM. But does anybody know the
details?
Basically, the JVM lacks a native ability to do tail calls. It does
not have an
instruction to remove/replace a stack frame without executing an
actual return
to the calling method/function.
With the heavy use of recursion in functional programs, this is an
important
feature in a language implementation to avoid stack overflows.
Some language implementations (Scala) can do partial workarounds by
turning
the generated code into a loop in the compiler, but this is frequently
limited
to only deal with self-recursive calls, and does not deal with the
general case
(X-calls-Y-calls-Z-calls-X...), which a proper implementation of tail-
calls at
the JVM level would allow.
At the JIT level (below the JVM spec level) some implementations may
actually do
the tail call optimization anyway, but this is beyond the control of a
language
implementation, and would result in a situation where the behaviour of
your
program depends on particular implementations/versions/parameters of
the JVM
running it. That is something to be avoided if possible.
Maarten Hazewinkel
maarten.hazewin...@gmail.com
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