I think you are confusing "partial application" and "partial evaluation". Though they are conceptually related. The former is what happens when you apply a function of arity N to M arguments, where M < N. In Haskell the partially applied function is suspended, pending the rest of its arguments. The latter is a way of taking a program and _some_ of its inputs and transforming/compiling/specialising it into a residual program, by "evaluating" as much as possible, given the inputs you have available. An interesting example of partial evaluation is to take an interpreter for a language and a sample source program, and partially evaluate the interpreter with respect to the program. The result is a version of the interpreter which acts effectively as a compiled version of the source program. In Hudak's paper(s), if I remember correctly, they have an interpreter for a functional language (in continuation passing style), which is parameterised by a monitor function. I think they are trying to argue that you can make the system more efficient if you partially evaluate the interpreter with respect to a particular monitor. It is better than running the interpreter directly. The problem is that I think it is hard to scale to a language like Haskell, though there might have been advances that I am not familiar with. Wikipedia has an entry on partial evaluation which is somewhat useful, though you should probably follow the references at the bottom. Cheers, Bernie.
-----Original Message----- From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe- bounces@haskell.org] On Behalf Of jim burton Sent: 21 March 2007 18:47 To: haskell-cafe@haskell.org Subject: [Haskell-cafe] Partial Evaluation
I am reading Hudak's paper Modular Domain Specific Languages and Tools [1] and am confused by his use of the term `Partial Evaluation'. I understand it to mean supplying some but not all arguments to a function, e.g. (+3) but it seems to mean something else too. This is in the context of optimising performance:
"We have used existing partial evaluation techniques to do this...Unfortunately, there does not currently exist a suitable, easy-to-use partial evaluator for Haskell. Our approach was to convert the Haskell program to Scheme, partially evaluate the Scheme program, and then translate back into Haskell."
What does P.E, mean here?
Thanks,
[1] Available http://wiki.ittc.ku.edu/lambda/Image:Hudak- Modular_Domain_Specific_Languages_and_Tools.pdf
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