2010/1/15 Simon Brooke <still...@googlemail.com>:
> OK, I'm trying to get seriously stuck in, and the first thing I'm
> trying to do is reimplement an inference engine I first wrote in
> Portable Standard Lisp and then in InterLisp-D in /idiomatic/ Clojure.
> So please have patience with me...
>
> If one has something which is strongly typed, is it idiomatic to make
> a Java class to hold it?
>
> I want a structure like this
>
> (defstruct feature :name :default)
>
> but I want in addition to constrain the binding of :name to be always
> a Clojure keyword and the binding of :default to be always a boolean -
> the Clojure values either true or false.
>
> I've tried
>
> (defstruct feature [#^Keyword :name] :default)
#^something applies to the thing to the right of it. There's no need
to enclose anything in square brackets. But this won't work here
anyway:
user=> (defstruct feature #^Keyword :name :default)
java.lang.IllegalArgumentException: Metadata can only be applied to IMetas
:default
java.lang.Exception: Unmatched delimiter: )
> but the reader spits an illegal argument exception. Is there different
> syntax which the reader could parse? Or am I using the wrong kind of
> thing?
>
> Of course given that a struct is immutable I could have a make-feature
> function which has type-hinted args:
>
> (defn
> #^{:doc "Make a feature safely"}
> make-feature [#^Keyword name #^bool default]
> (struct-map feature :name name :default default))
defn also supports docstrings more directly like this:
(defn make-feature
"Make a feature safely"
[...]
(struct-map ...))
> This works and does sort-of what I want - I can't guarantee that
Does it?
user=> (defn
#^{:doc "Make a feature safely"}
make-feature [#^Keyword name #^bool default]
(struct-map feature :name name :default default))
#'user/make-feature
user=> (make-feature "some name" 42)
{:name "some name", :default 42}
> nothing outside my make-feature function will make features but I
> don't think I need to. However, it feels clunky - I instinctively feel
> there must be a better way. Is this what deftype should be used for?
> If so, where is it documented? The book I'm using - Stuart Halloway's
> 'Programming Clojure' - doesn't seem to have it (or if it has I've
> missed it). Also, I don't seem to have deftype in my 1.1.0 rc3 build :
>
> cc.journeyman.dtree.dtree=> (doc deftype)
> java.lang.Exception: Unable to resolve var: deftype in this context
> (NO_SOURCE_FILE:20)
>
> I've also grepped the source code of clojure and failed to find it.
It's not in any official release yet. In your git checkout do
something like this to get it:
$ git checkout -b new origin/new
That will create a branch called "new" based on the "new" branch in
Rich's repository. Then you can "git pull" as usual to keep it
updated. If you want to switch back to master, just do "git checkout
master".
I've not tried deftype yet, so I don't know if it's what you're looking for.
--
Michael Wood <esiot...@gmail.com>
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