Thanks. But I have to turn it into a string before storing it in the database; when I tried to store a serialized list in it (in a VARCHAR field), it complained that it expected a string. That's where all the trouble came from. The trouble I had was parsing the string back into the serialized form, which 'with-input-from-string does (because, I presume, it treats the contents of the string as the input, rather than the string itself).
Of course, if there is a way to store serialized data directly in the database, that would be great - but -- except for arrays in a Postgre database -- that doesn't seem to be the case. On Tue, Mar 21, 2017 at 8:04 PM, Philip McGrath <phi...@philipmcgrath.com> wrote: > When you use: > (write (~a (serialize '((0 1) (1 0)))) out) > you are first turning the result of deserialize into a string, then > writing the string, so read will produce a string. > > Your example will work correctly if you drop the ~a and just use: > (write (serialize '((0 1) (1 0))) out) > > If that's less than totally clear, for illustrative purposes, consider the > following: > > (serialize '((0 1) (1 0))) > '((3) 0 () 0 () () (q (0 1) (1 0))) > > (~a '((3) 0 () 0 () () (q (0 1) (1 0)))) > "((3) 0 () 0 () () (q (0 1) (1 0)))" > > (with-output-to-string > (λ () (write "((3) 0 () 0 () () (q (0 1) (1 0)))"))) > "\"((3) 0 () 0 () () (q (0 1) (1 0)))\"" > > (with-input-from-string "\"((3) 0 () 0 () () (q (0 1) (1 0)))\"" > read) > "((3) 0 () 0 () () (q (0 1) (1 0)))" > > (with-output-to-string > (λ () (write '((3) 0 () 0 () () (q (0 1) (1 0)))))) > "((3) 0 () 0 () () (q (0 1) (1 0)))" > > (with-input-from-string "((3) 0 () 0 () () (q (0 1) (1 0)))" > read) > '((3) 0 () 0 () () (q (0 1) (1 0))) > > (deserialize '((3) 0 () 0 () () (q (0 1) (1 0)))) > '((0 1) (1 0)) > > On Tue, Mar 21, 2017 at 6:53 PM Marc Kaufmann <marc.kaufman...@gmail.com> > wrote: > >> Regarding not using deserialize directly: I may be using deserialize in >> the wrong way, but the following doesn't work (and I had tried that before >> posting): >> >> > (define-values (in out) (make-pipe)) >> > (write (~a (serialize '((0 1) (1 0))))) >> "((3) 0 () 0 () () (q (0 1) (1 0)))" >> > (write (~a (serialize '((0 1) (1 0)))) out) >> > (deserialize (read in)) >> ; car: contract violation >> ; expected: pair? >> ; given: "((3) 0 () 0 () () (q (0 1) (1 0)))" >> ; [,bt for context] >> >> 'read simply returns a string. On the other hand, using Philip's >> suggestion works (although I can't say I fully understand the subtleties >> involved): >> >> > (define serialized-string (~a (serialize '((0 1) (1 0))))) >> > (with-input-from-string serialized-string (lambda () (deserialize >> (read)))) >> '((0 1) (1 0)) >> >> Regarding pg-array, I thought (from the docs) that it allowed for >> multi-dimensional arrays, but since I might need a similar functionality >> for structs and the like, I thought that I should find another solution. >> >> Thanks everyone for the quick response. >> >> Cheers, >> >> Marc >> >> >> On Tue, Mar 21, 2017 at 5:58 PM, George Neuner <gneun...@comcast.net> >> wrote: >> >> On 3/21/2017 5:48 PM, Jon Zeppieri wrote: >> >> Ah, except apparently `pg-array` only supports arrays with dimension >> 1. So... that won't help. >> >> >> I *think* Ryan Culpepper fixed that a long time ago ... though the docs >> may never have been updated. I had a workaround at the time and >> unfortunately I never did go back to verify the fix in later releases. >> >> George >> >> >> On 12/18/2014 09:03 PM, George Neuner wrote: >> >> Using 6.0.1. I just painfully discovered that >> >> (pg-array->list (list->pg-array (list))) >> => ERROR >> pg-array->list: expected argument of type <pg-array of dimension 1>; >> given: (pg-array 0 '() '() '#()) >> >> The documentation for list->pg-array states that it produces an array >> of dimension 1. However, if you pass an empty list, you get back an array >> of dimension zero which you then can't transform back to a list [ except by >> going straight to the internal vector ]. >> >> My question is, "shouldn't these conversions be symmetric?" I >> understand an array with no elements is meaningless as an array, but >> Postgresql (ab)uses arrays as substitutes for lists and sets, so an empty >> array does have meaning. >> >> >> -- >> You received this message because you are subscribed to a topic in the >> Google Groups "Racket Users" group. >> To unsubscribe from this topic, visit https://groups.google.com/d/ >> topic/racket-users/xAbm8mlPX-w/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> racket-users+unsubscr...@googlegroups.com. >> >> >> For more options, visit https://groups.google.com/d/optout. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
