GNU Info

(elisp)Byte-Code Objects

---

Next: Disassembly Prev: Eval During Compile Up: Byte Compilation

---

Enter node , (file) or (file)node

Byte-Code Function Objects
==========================

   Byte-compiled functions have a special data type: they are
"byte-code function objects".

   Internally, a byte-code function object is much like a vector;
however, the evaluator handles this data type specially when it appears
as a function to be called.  The printed representation for a byte-code
function object is like that for a vector, with an additional `#'
before the opening `['.

   A byte-code function object must have at least four elements; there
is no maximum number, but only the first six elements have any normal
use.  They are:

ARGLIST
     The list of argument symbols.

BYTE-CODE
     The string containing the byte-code instructions.

CONSTANTS
     The vector of Lisp objects referenced by the byte code.  These
     include symbols used as function names and variable names.

STACKSIZE
     The maximum stack size this function needs.

DOCSTRING
     The documentation string (if any); otherwise, `nil'.  The value may
     be a number or a list, in case the documentation string is stored
     in a file.  Use the function `documentation' to get the real
     documentation string (Note: Accessing Documentation).

INTERACTIVE
     The interactive spec (if any).  This can be a string or a Lisp
     expression.  It is `nil' for a function that isn't interactive.

   Here's an example of a byte-code function object, in printed
representation.  It is the definition of the command `backward-sexp'.

     #[(&optional arg)
       "^H\204^F^@\301^P\302^H[!\207"
       [arg 1 forward-sexp]
       2
       254435
       "p"]

   The primitive way to create a byte-code object is with
`make-byte-code':

 - Function: make-byte-code &rest elements
     This function constructs and returns a byte-code function object
     with ELEMENTS as its elements.

   You should not try to come up with the elements for a byte-code
function yourself, because if they are inconsistent, Emacs may crash
when you call the function.  Always leave it to the byte compiler to
create these objects; it makes the elements consistent (we hope).

   You can access the elements of a byte-code object using `aref'; you
can also use `vconcat' to create a vector with the same elements.