Kawa: Bytevectors

Bytevectors

Bytevectors represent blocks of binary data. They are fixed-length sequences of bytes, where a byte is an exact integer in the range [0, 255]. A bytevector is typically more space-efficient than a vector containing the same values.

The length of a bytevector is the number of elements that it contains. This number is a non-negative integer that is fixed when the bytevector is created. The valid indexes of a bytevector are the exact non-negative integers less than the length of the bytevector, starting at index zero as with vectors.

The bytevector type is equivalent to the u8vector uniform vector type, but is specified by the R7RS standard.

Bytevectors are written using the notation #u8(byte . . . ). For example, a bytevector of length 3 containing the byte 0 in element 0, the byte 10 in element 1, and the byte 5 in element 2 can be written as following:

#u8(0 10 5)

Bytevector constants are self-evaluating, so they do not need to be quoted in programs.

Type: bytevector

The type of bytevector objects.

Constructor: bytevector byte …

Return a newly allocated bytevector whose elements contain the given arguments. Analogous to vector.
(bytevector 1 3 5 1 3 5)  ⇒  #u8(1 3 5 1 3 5)
(bytevector)  ⇒  #u8()

Procedure: bytevector? obj

Return #t if obj is a bytevector, #f otherwise.

Procedure: make-bytevector k

Procedure: make-bytevector k byte

The make-bytevector procedure returns a newly allocated bytevector of length k. If byte is given, then all elements of the bytevector are initialized to byte, otherwise the contents of each element are unspecified.
(make-bytevector 2 12) ⇒ #u8(12 12)

Procedure: bytevector-length bytevector

Returns the length of bytevector in bytes as an exact integer.

Procedure: bytevector-u8-ref bytevector k

It is an error if k is not a valid index of bytevector. Returns the kth byte of bytevector.
(bytevector-u8-ref ’#u8(1 1 2 3 5 8 13 21) 5)
  ⇒ 8

Procedure: bytevector-u8-set! bytevector k byte

It is an error if k is not a valid index of bytevector. Stores byte as the kth byte of bytevector.
(let ((bv (bytevector 1 2 3 4)
  (bytevector-u8-set! bv 1 3)
  bv)
  ⇒ #u8(1 3 3 4)

Procedure: bytevector-copy bytevector [start [end]]

Returns a newly allocated bytevector containing the bytes in bytevector between start and end.
(define a #u8(1 2 3 4 5))
(bytevector-copy a 2 4))
    ⇒ #u8(3 4)

Procedure: bytevector-copy! to at from [start [end]]

Copies the bytes of bytevectorfrom between start and end to bytevector to, starting at at. The order in which bytes are copied is unspecified, except that if the source and destination overlap, copying takes place as if the source is first copied into a temporary bytevector and then into the destination. This is achieved without allocating storage by making sure to copy in the correct direction in such circumstances.

It is an error if at is less than zero or greater than the length of to. It is also an error if (- (bytevector-length to) at) is less than (- end start).
(define a (bytevector 1 2 3 4 5))
(define b (bytevector 10 20 30 40 50))
(bytevector-copy! b 1 a 0 2)
b        ⇒ #u8(10 1 2 40 50)

Procedure: bytevector-append bytevector...

Returns a newly allocated bytevector whose elements are the concatenation of the elements in the given bytevectors.
(bytevector-append #u8(0 1 2) #u8(3 4 5))
        ⇒  #u8(0 1 2 3 4 5)

Procedure: utf8->string bytevector [start [end]]

This procedure decodes the bytes of a bytevector between start and end, interpreting as a UTF-8-encoded string, and returns the corresponding string. It is an error for bytevector to contain invalid UTF-8 byte sequences.
(utf8->string #u8(#x41))  ⇒ "A"

Procedure: string->utf8 string [start [end]]

This procedure encodes the characters of a string between start and end and returns the corresponding bytevector, in UTF-8 encoding.
(string->utf8 "λ")     ⇒ " #u8(#xCE #xBB)