Maybe the JVM could be abused so that all of the haskell code is
within one "function", so as to avoid java's notion of a function
boundary and implement our own using just goto? Or does the JIT
operate on entire functions at a time?
On Fri, Jun 26, 2009 at 1:23 PM, John A. De Goes
JVM 7 has tail calls, and if you don't want to wait for that, "goto" works perfectly well for self-recursive functions. Other techniques can deal with mutual recursion, albeit at the cost of performance.
Regards,
John A. De Goes N-Brain, Inc. The Evolution of Collaboration
http://www.n-brain.net | 877-376-2724 x 101
On Jun 26, 2009, at 6:26 AM, Maarten Hazewinkel wrote:
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.hazewinkel@gmail.com
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