Re: [potluck dish] the (potluck struct) module

[Matt Wette]

First message got garbled.  Redo:

If you have used the Python struct module then this will look familiar.

Otherwise, check out https://docs.python.org/2/library/struct.html

Attached are three files:

* struct.scm: the source code 

* struct.texi: documentation 

* struct.test: test code

Struct Module

=============

The '(potluck struct)' module provides procedures for packing and

unpacking scheme data to and from bytevectors based on a format string.

     (use-modules (potluck struct))

     ;; pack two unsigned shorts and a double float in big endian order

     (define data (pack ">2Hd" 3 22 34.0))

     (write data) (newline)

     ==>

     #vu8(0 3 0 22 64 65 0 0 0 0 0 0)

     ;; verify using unpack

     (write (unpack ">2Hd" data)) (newline)

     ==>

     (3 22 34.0)

 -- Scheme Procedure: pack format vals ...

     Return a bytevector that contains encoded data from VALS, based on

     the string FORMAT.

 -- Scheme Procedure: unpack format bvec

     Return a list of scheme objects decoded from the bytevector BVEC,

     based on the string FORMAT.

 -- Scheme Procedure: packed-size format

     Return the number of bytes represented by the string FORMAT.

   The _format_ string used for PACK and UNPACK is constructed as a

sequence of digits, representing a repeat count, and codes, representing

the binary content.

The string may optionally begin with a special character that represents

the endianness:

    =        native endianness

    <        little-endian

    >        big-endian

    !        network order -- i.e., big-endian

Type codes used in the format string are interpreted as follows:

    x        blank byte

    c        8-bit character

    ?        boolean

    b        signed 8-bit integer

    B        unsigned 8-bit integer

    h        signed 16-bit integer

    H        unsigned 16-bit integer

    i        signed 32-bit integer

    I        unsigned 32-bit integer

    l        signed 32-bit integer

    L        unsigned 32-bit integer

    q        signed 64-bit integer

    Q        unsigned 64-bit integer

    f        32-bit IEEE floating point

    d        64-bit IEEE floating point

    s        string

   The following issues remain to be addressed:

string padding

     'pack' assumes that the string length in the format is the same as

     in the passed string.  Non-conformance is not trapped as an error.