iasc-stm-rehs: A Haskell repository from AgustinCroce

Requirements

You need to install stack first.

Starting the server

Simply run ./start.sh. This command will compile and start your project.

Starting the client

There is no client 😛. But we have telnet:

franco@xinaiu:~/tmp/ping-pong-hs$ telnet localhost 3500
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
read

set:hello
hello
read
hello
set:world
world
read
world
clear

read

set:persistent
persistent
quit
Connection closed by foreign host.
franco@xinaiu:~/tmp/ping-pong-hs$ telnet localhost 3500
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
read
persistent

As you can see, data is persistent thanks to STM and IO

The goal

Our server is quite limited, it is a table of just one unnamed slot. We want to extend it so that it works with multiple slots and has richer operations:

franco@xinaiu:~/tmp/ping-pong-hs$ telnet localhost 3500
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
schema:name:surname:house
<OK>
read:name

set:name:jon
jon
set:lastname:snow
snow
set:house:stark
stark
clear:lastname

set:lastname:spoiler
spoiler
clear_all
read:lastname

read:name

read:house

set:name:arya
arya
reverse:name
ayra
upcase:name
AYRA

The goal of this project is to extend this code so that the previous commands work.

Tips

Read this: https://www.reddit.com/r/haskell/comments/25xyts/how_about_an_stm_hash_table_implementation/.
You can implement the table as an inmutable list of string keys and (mutable) TVar values.
The schema operation may destroy all data.
don't try to change Main and Server alot. Intead, focus on the Rehs module, which declares its transactional primitive functions, and Commands module, which parses strings into transactions.
notice that Rehs.Server and Rehs.IO actually deal with IO, but other modules just work with STM and pure functions. If you start to write many IO functions, you are probably doing it wrong.

Going further