On 09/06/13 18:54, Matthias Felleisen wrote:
(define item (first items))
(define weight (item-weight item))
(define volume (item-volume item))
(define value (item-value item))
Now I understand that the three lines of extracting the content of the
first struct are painful. While I understand and agree with the match
here, I have also experimented with a struct-open construct for my
latest project, and I find this code as readable as the one with match:
I also find structs quite cumbersome to use, although infinitely better
than (define name (first item)) etc.
Is there a lot of work going into structs at the moment?
I find them particulary hard to use in a purely functional (non-mutable)
way, since there is no shorthand way of copying a struct. AFAICT, at the
moment, to copy an item I need to:
(struct item (name explanation value weight volume) #:prefab)
(define gold (item "gold (bars)" "Shiney shiney" 2500 2.0 0.002))
(define fools-gold
(item
(item-name gold)
(item-explanation gold)
2.50
(item-weight gold)
(item-volume)))
Possibly with some variation on extracting the fields, using match or
whatever. Even with a match, you still need to evaluate each of the
fields; and if I want to copy one field from an n-field struct, I need n
field accessors, and n fields in the constructor (with one of them
modified).
What I would really like to have is the following defined by (struct item):
(define fools-gold (copy-item gold #:value 2.50))
Am I missing a trick?
Tim
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