1. syntax-let-optionals*
2. define-binary-record-type
3. defrec

Defines a new record type that supports serializing to and from binary ports. The generated procedures accept keyword-style arguments:

• (make: <constructor-name>)
• (pred: <predicate-name>)
• (read: <reader-name>)
• (write: <writer-name>)
• (block: <fields> ...)

The fields are also similar to define-record-type but with an additional type:

(field (type args ...) getter setter)

Built-in types include:

• (u8) - a single byte in [0, 255]
• (u16/le) - a little-endian short integer
• (u16/be) - a big-endian short integer
• (fixed-string <length>) - a fixed-length utf-8 string
• (padded-string <length> (pad <pad-char>)) - a utf-8 string padded to a given length
• (octal <length>) - an integer in octal string format
• (decimal <length>) - an integer in decimal string format
• (hexadecimal <length>) - an integer in hexadecimal string format

In addition, the field can be a literal (char, string or bytevector), for instance as a file magic sequence or fixed separator. The fields (and any constants) are serialized in the order they appear in the block. For example, the header of a GIF file could be defined as:

 (define-binary-record-type gif-header
   (make: make-gif-header)
   (pred: gif-header?)
   (read: read-gif-header)
   (write: write-gif-header)
   (block:
    "GIF89a"
    (width (u16/le) gif-header-width)
    (height (u16/le) gif-header-height)
    (gct (u8) gif-header-gct)
    (bgcolor (u8) gif-header-gbcolor)
    (aspect-ratio (u8) gif-header-aspect-ratio)
    ))

ERROR on line 26 of file lib/srfi/9.scm: immutable binding: gif-header

For a more complex example see the (chibi tar) implementation.

The binary type itself is a macro used to expand to a predicate and reader/writer procedures, which can be defined with define-binary-type. For example,

 (define-binary-type (u8)
   (lambda (x) (and (exact-integer? x) (<= 0 x 255)))
   read-u8
   write-u8)