Hi John, Thanks for your feedback. It would be preferable to use regular parentheses to delimit the section, but it could only work in special cases. Consider this expression using free sections: map _[ f (g __ y) ]_ bs If that were written "map (f (g __ y)) bs" and parentheses used to delimit the freesect, that would give you the equivalent of map ( f _[ g __ y ]_ ) bs which is incorrect (doesn't type). Also, one may want more than a single free section in a RHS, which would not be possible without distinct grouping syntax. I looked into some sort of default context inference (like, the tighest grouping which passes the type check), but that gets fairly complicated and might still result in ambiguity, in case more than one possible grouping types correctly. I also set out originally to overload the single-underscore for wildcard, but was unsuccessful (reduce/reduce conflicts in the HSE parser), so I settled on double-underscore which I've come to think preferable. As I said on the linked web page, I'm still exploring default context inference (for interest's sake), and if anyone can suggest a nice way to use SYB to compute the join (in the semilattice sense) of all terms in a constructed tree which have type T, I'd really like to see that... -Andrew On Thu, Mar 1, 2012 at 10:01 PM, John Lask <jvlask@hotmail.com> wrote:

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On Wed, Feb 29, 2012 at 9:27 PM, Ras Far<rasfar@gmail.com>  wrote:

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Hello,

I bit premature perhaps but I wanted to post it on a leap day...

http://fremissant.net/freesect

Thanks for eyebloom on #haskell for motivating me to finally implement an old idea.  Thanks to the rest on #haskell for doing their best to talk me out of it. ;)

I make no claims regarding the usefulness of the extension, but some folks might find it interesting, or may just appreciate additional examples of using HSE and SYB.  I regret that I am not a better Haskell coder, but it is what it is!

Kind Reg'ds, Andrew Seniuk (rasfar)

why couldn't you use standard brackets ( to delimit the extent ? I suppose that would have added complexity to the syntax analysis, however I think it would have been (in my mind) neater.

On 3/3/12 7:55 PM, AntC wrote:

So is there an arbitrary greek letter term for reordering?

I'm not aware of one, in part no doubt because it's not a semantics-preserving transformation (that is, not in the same sense as that used in defining alpha, beta, eta, delta,...). In the extension to lambda calculus I presented at NASSLLI a couple years back[1] it is indeed semantics-preserving. In that context I named it chi, because it's a chiastic transformation. Though do note that the calculus also supports an alternative interpretation of reordering, dubbed ksi (for, er, "ksiastic" transformations?). That is, when accounting for reordering we can either reorder the abstractions (chi) or we can reorder the applications (ksi); in many contexts it is impossible to distinguish them on pretheoretical grounds, though there are places where they diverge. For the record, renaming variables is usually called "alpha-variance" and the alpha-equivalence relation is "modulo alpha-variance". ("Modulus" is a noun; "modulo" is, in English, a preposition.) [1] http://llama.freegeek.org/~wren/pubs/ccgjp_nasslli2010.pdf -- Live well, ~wren