On Mon, Jul 26, 2010 at 14:43, Matthew Flatt <[email protected]> wrote:
> At Mon, 26 Jul 2010 14:29:57 +0200, Laurent wrote: > > The reader cannot read #<path:....> forms (is this the right term?). > > When the interaction window is in constructor mode, for (build-path "a" > > "b"), it writes #<path:a/b>, but this cannot be read back. > > > > First question: would it be possible to make the reader read paths? > > The reason that paths are not `read'able is that's there is not a > single right choice for how to marshal paths: > > * Sometimes you want the string form of a path, which may be encoded > in different ways on different platforms (e.g., using different > locales) to keep the string form the same. > > * Sometimes you want the bytes form of a path, because the path isn't > going to be used on multiple systems, and converting to a string > form may lose information (e.g., because it's not a UTF-8 encoding). > > Since there was no right answer, we decided not to pick either of them. > The lack of a `read'able form is a weak hint to programmers that they > need to look closely at the question. > Thanks, I understand. Maybe we could distinguish between `read'able and un`read'able paths? > > > Second question: I need this for my own purposes, so I wrote a > > path-constructor: > > (define/provide (write-path p) > > (cons 'build-path > > (map (λ(p-elt)(if (symbol? p-elt) > > (list 'quote p-elt) > > (path->string p-elt))) > > (explode-path p)))) > > > > > (write-path (build-path 'same 'up "a" "b")) > > '(build-path 'same 'up "a" "b") > > > > Does someone know if this is good enough, or am I omitting something > > (platform specific maybe)? > > As a minimum, use `path-element->string' instead of `path->string'. > > Otherwise, beware that (as noted above) not all paths have string > encodings; depending on your application, that may not be an issue. Or > it may be that you want to marshal via byte strings using `bytes->path' > as a constructor. > Thanks a lot Matthew!
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