Selecting Bit String Components (MIT/GNU Scheme 10.1.1)

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### 9.2 Selecting Bit String Components

procedure: bit-string? object

  Returns `#t` if object is a bit string; otherwise returns `#f`.

procedure: bit-string-length bit-string

  Returns the length of bit-string.

procedure: bit-string-ref bit-string k

  Returns `#t` if the kth bit is 1; otherwise returns `#f`. K must be a valid index of bit-string.

procedure: bit-string-set! bit-string k

  Sets the kth bit in bit-string to 1 and returns an unspecified value. K must be a valid index of bit-string.

procedure: bit-string-clear! bit-string k

  Sets the kth bit in bit-string to 0 and returns an unspecified value. K must be a valid index of bit-string.

procedure: bit-substring-find-next-set-bit bit-string start end

  Returns the index of the first occurrence of a set bit in the substring of bit-string from start (inclusive) to end (exclusive). If none of the bits in the substring are set `#f` is returned. The index returned is relative to the whole bit string, not substring.

  The following procedure uses `bit-substring-find-next-set-bit` to find all the set bits and display their indexes:

      (define (scan-bitstring bs)
        (let ((end (bit-string-length bs)))
          (let loop ((start 0))
            (let ((next
                   (bit-substring-find-next-set-bit bs start end)))
              (if next
                  (begin
                    (write-line next)
                    (if (< next end)
                        (loop (+ next 1)))))))))