[plt-dev] feature request

This is probably obvious but you could write a pretty simple function
to build the prefab struct out of the sexp and even put it in a
library to be used as a replacement for read.

Robby

On Wednesday, April 14, 2010, Eli Barzilay <eli at barzilay.org> wrote:
> On Apr 14, Matthias Felleisen wrote:
>> A lot of libraries read in file content as lists (or S-expressions)
>> of list-based structures (see csv on planet for one example, which I
>> am currently incorporating to a small degree into
>> 2htdp/batch-io). If I had this structure -- including in teaching
>> languages -- I could easily 'view' these S-expressions/lists as
>> structs, making for much more readable code.
>
> +1 for the use case (but I don't have an opinion on whether it
> justifies implementing them or not).  And here is how you do it in CL:
>
> Plain list -- with the default keyworded constructor
>
>   CL-USER(1): (defstruct (foo (:type list)) x y)
>   FOO
>   CL-USER(2): (make-foo :y 2 :x 1)
>   (1 2)
>   CL-USER(3): (foo-x (list 1 2))
>   1
>
>
> Tagged list, with a positional constructor with arguments in reverse
>
>   CL-USER(4): (defstruct (foo (:type list) :named (:constructor mkfoo (y x)))
>                 x y)
>   FOO
>   CL-USER(5): (mkfoo 2 1)
>   (FOO 1 2)
>   CL-USER(6): (foo-p '(1 2))     ; ("-p" is a bad spelling for "?")
>   NIL
>   CL-USER(7): (foo-p '(foo 1 2))
>   T
>   CL-USER(8): (foo-x (mkfoo 2 1))
>   1
>
>
> --
>           ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
>                     http://barzilay.org/                   Maze is Life!
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