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.