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Erlang Trim Thu, 11 Feb 2010 13:30:13 -0500

This is a nice piece of code that I stumbled upon a few months ago while wanting to string the white space off the end of a string. Thanks go to Steve Davis for his contribution.


-module(trim).
-author('Steve Davis < steven · charles · davis ? gmail · com >').
-export([trim/1]).

trim(Bin) when is_binary(Bin) ->
    list_to_binary(trim(binary_to_list(Bin)));
trim(String) when is_list(String) ->
    String2 = lists:dropwhile(fun is_whitespace/1, String),
    lists:reverse(lists:dropwhile(fun is_whitespace/1, lists:reverse(String2))).

is_whitespace($\s) -> true;
is_whitespace($\t) -> true;
is_whitespace($\n) -> true;
is_whitespace($\r) -> true;
is_whitespace(_Else) -> false.

Keywords:
notes
quick tips
erlang

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Getting Around ODBC slow connection pooling in Erlang Mon, 10 Aug 2009 10:32:03 -0400

If your like me you use SQL quite a bit, or least for some form of data source. One of the most portable methods for SQL interfacing is to use some form of abstraction, this adds portability as well as some support (sometimes). In this case I'm using Erlang to query a bunch of data out of a database and I want to do this very very quickly and efficiently

I've read only that ODBC v3 is supposed to support connection pooling by default, however on my PC (ubuntu hardy) is slow as heck and has a long latency time for initializing connections. However I was able to come up with a way around this by creating a process that does nothing but SQL functions. The below example should be all you need to start using this yourself.


-module(fetcher).
-author("Brian Smith").
-export([start, loop0/0, loop0/1, query/1]).

-define(DSN, "dsn=myodbc3").

start() ->
    register(fetcher_pid, spawn(?MODULE, loop0, [])).

loop0() ->
    {ok, DbConn} = odbc:connect(?DSN, []),
    loop0(DbConn).
loop0(DbConn) ->
    receive
        {sql, From, SqlStmt} ->
             From ! odbc:sql_query(DbConn, SqlStmt),
             loop0(DbConn);
        quit ->
             odbc:disconnect(DbConn),
             quit
    end.

query(SqlStmt) ->
   fetcher_pid ! {sql, self(), SqlStmt},
   receive
        _Results ->
                 _Results
   end.

To use you just need to run fetcher:start().. I'm still trying to figure out how to block the pid for receiving SQL queries until odbc:connect() is complete, so any ideas on this is appreciated.

Keywords:
work
notes
quick tips
erlang

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DJB2 String Hashing Algorithm Implemented in Erlang Wed, 29 Jul 2009 15:53:45 -0400

Erlang is a very interesting functional programming language that has been receiving a fair amount of attention lately. So I've been playing with it off and on as my little fun project for educating myself. So to give back here is a simple DJB2 hashing algorithm implemented in Erlang.

Something I have had problems with before when implementing DJB2 in those languages (such as Python) is the native infinite precision integers of those languages. However by bitwise AND logic the result of the hash against the maximum value of a C unsigned long negates that by truncating the result buffer so we remain using the proper number of bits for the hashing.


-module(djb2).
-author('Brian Smith http://www.modernninja.com/').
-export([hash/1, djb2/2]).

-define(INIT_HASH, 5381).

hash(String) -> djb2(String, ?INIT_HASH).

djb2([], Hash) -> Hash;
djb2([Head|Rest], Hash) -> djb2(Rest, (((Hash bsl 5) + Hash) + Head) band 16#FFFFFFFF).

Keywords:
notes
quick tips
erlang

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