Miscellaneous J scripts

This project was made as a class project for a systems programming class at the ITMO university. A report in Russian giving a short introduction to the J language and describing in somewhat more detail the code is available as report.pdf.

C FFI with J

J has quite minimalistic C FFI capabilities, namely '<library> <funtion> <signature>' cd '<arg1> <arg2>..' allows to call a function in a shared library, memr addr, offset, num [,size] allows to read data form addr + offset*size to addr + offset + num*size.

The cffi library extends the capabilities of J by adding functions to work with arbitrary C types and structures.

Here is an example usage:

NB. rep is a pointer to redisReply
len =. rep extract_size_t  'redisReply';'len'
ptr =. rep extract_pointer 'redisReply';'str'
ptr read_str len NB. returns the string

Redis

The following functions are implemented:

• redisConn addr;port - returns a pointed to redisContext, addr and pert are the address and port of the redis server.
• redisFree - frees a redisContext
• redisCmd ctx;cmd - executes a redis command and returns a result.

redisCmd is implemented using a lower level API:

• redisCommand ctx;cmd - executes a redis command and returns a redisReply.

• freeReplyObject - frees a redisReply.

• reply_str_i, reply_num_i, reply_array_i - extracts string/number/array data form a redisReply structure.

• reply_auto_i - extracts data form a redisReply structure guessing it's type.

Example usage:

'err ctx' =: redisConn '127.0.0.1';6379
if. err = 0 do.
  r =: redisCmd ctx; 'PING' NB. r = 'PONG'
  r =: redisCmd ctx;'INCR counter' NB. r = 1
end.
redisFree ctx