On Wed, Sep 14, 2011 at 5:58 AM, Leonardo Borges
<leonardoborges...@gmail.com> wrote:
> (defn neighbors
> ([size yx] (neighbors [[-1 0] [1 0] [0 -1] [0 1]] size yx))
> ([deltas size yx]
> (filter (fn [new-yx]
> (every? #(< -1 % size) new-yx))
> (map #(map + yx %) deltas))))
>
> This syntax made me scratch my head since I believe it was the first
> time I saw it.
In case it wasn't clear from Chouser's response, the key difference is
that this declares two versions of neighbors, one that takes three
arguments and one that takes four - essentially overloading on arity.
Here's an example from some of our code at World Singles:
(defn save-row
"Given a table name (string), a record and an optional
key-gen function, either insert it after applying the
key-gen function (if no pk) or update it. In both
cases, return the pk. The default key-gen function
is a no-op (identity).
When operating on a MongoDB collection, the logic is
much simpler because the pk is always :_id and key
generation is always handled by MongoDB. Also, we
always return the entire updated record (since we
can run functions against the database)."
([table record] (save-row table record identity :id 0))
([table record key-gen] (save-row table record key-gen :id 0))
([table record key-gen pk] (save-row table record key-gen pk 0))
([table record key-gen pk retry]
...))
Mostly we call this as (save-row :table-name {:some "record"}) but we
can also supply a key generation function (save-row :table-name {:some
"record"} add-uuid), for tables that don't have a generated PK column,
and we can specify the PK name if it isn't :id (save-row :table-row
{:some "record"} identity :email).
Ignore retry - we need to refactor that into a private helper function
:) It's part of the machinery that let's automatically retry
operations on MongoDB if the replica set has no active primary node
since it can take a while to failover...
Hope that helps?
--
Sean A Corfield -- (904) 302-SEAN
An Architect's View -- http://corfield.org/
World Singles, LLC. -- http://worldsingles.com/
Railo Technologies, Inc. -- http://www.getrailo.com/
"Perfection is the enemy of the good."
-- Gustave Flaubert, French realist novelist (1821-1880)
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