Function cells

[David C. Plummer <DCP@SCRC-QUABBIN.ARPA>]

    Date: Wed, 19 Feb 86 15:40 EST
    From: Guy Steele <gls@THINK-AQUINAS.ARPA>

    My memory is that a question arose as to whether, given that function
    cells and value cells were to be distinct, they should have identical
    binding mechanisms or not.  There was no compelling reason to allow
    special binding of function names, and the following argument was
    advanced against such special bindings: multiprocessing implementations
    of Lisp might well prefer to use deep special binding, and it was
    undesirable to have to deal with the deep binding mechanism for function
    lookups, given that most function-name references, unlike most
    variable-name references, occur free.  I recall that this was the
    deciding argument that eliminated special binding of function names from
    Common Lisp, thereby making function names and variable names dissimilar
    in their semantics and further discouraging their merging.

This is one reason I usually give people who ask me.  Consider another
reason: Suppose you allowed deep binding of function cells as 'part of
the language'.  What would happen if you bound #'CAR?  Doesn't this
effectively force every function to be a true function, even if the
hardware happens to be able to do the operation 10+ times faster than it
takes to do a function call?  'Well, you aren't allowed to (deep) bind
inline functions or functions that compile into instructions.' isn't a
good answer because then we have to agree on what these are, and we
might as well not be a portable language any more.

    I can report that much of the time I am very happy to have the two names
    spaces be distinct.  I get very unhappy whenever I find myself inventing
    functionals (functions that take other functions as arguments or return
    other functions as values) for various purposes.  For example, I have
    found it semantically convenient to do so in Connection Machine Lisp.
    In these situations I find the need for interpolated occurrences of
    "funcall" and "#'" extremely annoying.

I read this last paragraph 3 times and am under the impression you
change your mind on each sentence.  I'm really curious what you meant!