[Haskell-cafe] The Worker/Wrapper Transformation

Isaac Dupree isaacdupree at charter.net
Thu Jan 3 07:46:32 EST 2008

Achim Schneider wrote:
> ...is a paper about automatic specialisation of functions by unboxing
> arguments, one could say. I'm only on page 6, but already survived the
> first formalisms, which is bound to mean that the rest of the paper is
> likewise accessible, as hinted on at ltu.
> http://www.cs.nott.ac.uk/~gmh/wrapper.pdf
> The transformation itself is mindbogglingly easy, which makes this a
> good start: You only have to understand the formalisms, not so much what
> the formalisms are representing. To quote spj: It usually turns out to
> be more interesting and challenging than it seemed at first.
> I'm tempted to write that this is a paper for everyone trying to figure
> out what the heck Jonathan is talking about.

I like it!  Of course the technique itself doesn't provide guidance on 
what type you want to transform a function to.

on page 6, stronger vs weaker seemed backwards to me... isn't (wrap ◦ 
unwrap = idA) a stronger condition than (wrap ◦ unwrap ◦ body = body), 
because it tells you more, and is true in fewer cases? (which is also 
why you want to assume (wrap ◦ unwrap = idA) when you can, because it's 
the most useful one for subsequent program transformation)

and then the inevitable minor copy-editing :-)

p. 22. intentional properties --> intensional (right?)

p. 27. typo 'unwarp' for 'unwrap'

BTW. GHC currently does allow e.g. (I# (1# +# 2#)), not just (case (1# 
+# 2#) of n# -> I# n#) -- the strictness implications seem pretty 
straightforwards (it's trivial to transform away).

p. 29. "in both these system" -> systems


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