Hi,
as David has said, your macro works only for literal
values, which doesn't make much sense.. I would
implement i-let as follows:
(defmacro let-default
[bindings & body]
`(let ~(vec (mapcat (fn [[sym value default]]
`(value# ~value
~sym (if (nil? value#)
~default
value#)))
(partition 3 bindings)))
~...@body))
Please note also like Laurent stated, that the `or`
trick doesn't really work on such such a general
macro or you will be limited to non-boolean values!
This leads to the need of `if`. And this in turn leads
to the need of `gensym` (via #), because otherwise
the "value" is computed twice.
As for the question for the return type of the seq
functions: Returning a seq allows them to be lazy.
This is not only an issue of the input (the eg. vector
is already in the memory anyway), but also of the
number of traversals. Consider the following:
(map dec (filter #(> % 5) (map inc (some-vector here))))
Would map and filter return vectors because the
input is a vector, the following would happen:
1. map traverses the vector, incs its elements and
creates a new vector
2. filter traverses the new vector, removes elements
eventually and creates a new vector
3. map traverses the new vector, decs its elements
and creates a new vector
So you basically traversed the vector 3 times. While
in the current setup (wrapping the chain in an explicit
`vec`) traverses the vector only once. Minor issue:
you create more garbage in form of temporary vectors
which are thrown away almost immediately.
Hope this helps.
Sincerely
Meikel
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
-~----------~----~----~----~------~----~------~--~---
