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This SRFI defines a set of procedures for creating, accesing, and manipulating uniform vectors of bytes.
A number of applications deal with sequences of bytes, most prominently interfaces to C and I/O. Vectors are typically too space-costly and too slow to work well in these circumstance. This justifies having a separate type for byte vectors.
This SRFI is related to SRFI 4 (Homogeneous numeric vector datatypes), which also provides vectors of bytes. However, the extension described here does not require any extensions to the syntax of the underlying Scheme system.
The interface described here is identical to that offered by the
byte-vectors structure in Scheme 48.
Byte vectors are objects of a new type. This type may or may not be disjoint from the type of regular vectors.
As with vectors, the length of a byte vector is the number of elements it contains. This number is fixed. A valid index into a byte vector is an exact, non-negative integer. The first element of a byte vector has index 0, the last element has an index one less than the length of the vector.
(byte-vector? obj)Returns #t if obj is a vector, otherwise
returns #f. Analogous to vector?.
(make-byte-vector k
fill)Returns a newly allocated byte vector of size k
elements. Each element is initialized to fill.
Fill must be an exact integer in the range [0,255]. Analogous
to make-byte-vector.
(byte-vector byte ...)Returns a newly allocated byte vector whose elements contain the
given arguments, which must all be exact integers in the range [0,255].
Analogous to
byte-vector.
(byte-vector-length
byte-vector)Returns the number of elements in byte-vector as an
exact integer. Analogous to vector-length.
(byte-vector-ref byte-vector
k)k must be a valid index of byte-vector.
Byte-vector-ref returns the contents of element k
of byte-vector. Analogous to vector-ref.
(byte-vector-set! byte-vector k
byte)k must be a valid index of byte-vector.
Byte-vector-set! stores byte in element
k of byte-vector. The number of return values and
the return values is unspecified. However, the number of return values is
such that it is accepted by a continuation created by begin.
Analogous to vector-ref.
This reference implementation makes use of SRFI 9 (Defining Record Types) and SRFI 23 (Error reporting mechanism).
(define-record-type :byte-vector (really-make-byte-vector elements)
byte-vector? (elements byte-vector-elements))
(define (ensure-byte thing)
(if (not (and (integer? thing)
(exact? thing)
(>= thing 0)
(<= thing 255)))
(error "not a byte" thing)))
(define (make-byte-vector k fill)
(ensure-byte fill)
(really-make-byte-vector (make-vector k fill)))
(define (byte-vector . bytes)
(for-each ensure-byte bytes)
(really-make-byte-vector (apply vector bytes)))
(define (byte-vector-length byte-vector)
(vector-length (byte-vector-elements byte-vector)))
(define (byte-vector-ref byte-vector k)
(vector-ref (byte-vector-elements byte-vector) k))
(define (byte-vector-set! byte-vector k byte)
(ensure-byte byte)
(vector-set! (byte-vector-elements byte-vector) k byte))
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