Re: byte-opt.el addition - optimize list of compile-time constants

[Zack Weinberg]

Stefan Monnier <address@hidden> writes:

>> I seriously wonder how much would break if this optimization were
>> implemented for 'list'.  My suspicion is that people don't commonly
>> apply 'eq' to lists in the first place.
>
> Well, try it:
>
>   (put 'list 'byte-optimizer 'byte-optimize-pure-func)
>   (put 'list* 'byte-optimizer 'byte-optimize-pure-func)
>   (put 'cons 'byte-optimizer 'byte-optimize-pure-func)
>   (put 'append 'byte-optimizer 'byte-optimize-pure-func)

I checked out CVS Emacs and tried this, and it fails catastrophically
during bootstrap; so I guess my intuition was wrong.  Optimizing list
or append with byte-optimize-pure-func causes errors like the following:

    In byte-optimize-lapcode:
    byte-opt.el:1748:45:Warning: `t' called as a function
    byte-opt.el:1970:52:Warning: `nil' called as a function

    In end of data: byte-opt.el:2044:1:Warning: the following
    functions are not known to be defined: t, nil

and optimizing cons causes

    In toplevel form:
    ../../emacs/lisp/emacs-lisp/byte-opt.el:1508:45:Error: Wrong type
    argument: sequencep, 0

-- both of these are from compiling byte-opt.el from 'make bootstrap'.

I'm interested in debugging this, but I don't know how to proceed.

I'll also point out that this does not solve the problem I am
interested in solving; with list optimized via
byte-optimize-pure-func, debug-on-entry byte-optimize-pure-func and
then execute

(disassemble 
  (lambda nil 
    `(:a 1 :b 2 
      :c #'(lambda nil (when (eq (following-char) ?\n) (forward-char 1))))))

and

(disassemble 
  (lambda nil 
    `(:a 1 :b 2 
      :c ,#'(lambda nil (when (eq (following-char) ?\n) (forward-char 1))))))

In the first case, byte-optimize-pure-func is never called and the
inner function is not compiled (I assume this is because ` is being
optimized to ' when there is no , or ,@ anywhere in its form).  In the
second place, byte-optimize-pure-func is called, but the optimization
fails because a (function ...) form appears inside the arguments to
list, which does not count as byte-compile-constp.  This is the other
problem I mentioned earlier - at the point at which the
'byte-optimizer function for list is called, the inner function has
not yet been compiled, contrary to the general principle that the byte
optimizer operates depth-first.

zw