EOF-VALUE

[Christopher Fry <cfry@OZ.AI.MIT.EDU>]

    What is the default value of EOF-VALUE for all the read functions?

    For example, READ takes (&Optional input-stream eof-error-p eof-value).

    If only INPUT-STREAM and EOF-ERROR-P are supplied, and EOF-ERROR-P is non-nil,
    CLtL says that the value of EOF-VALUE will be returned if an end-of-file 
    is found.  Without any further specification, I must assume that it
    defaults to NIL, which is the default default value for unsupplied &Optionals.

    For READ-CHAR, and READ-BYTE, NIL is an impossible value, but for READ
    and company, NIL is a perfectly reasonable return value.
    Thus, it makes no sense to supply a non-nil second argument, but not the third.  
    In fact, the only safe value for EOF-VALUE in these cases is some
    non-atomic object that could never be EQ to something read in.  

    For this reason, In just about every file that calls read, I've got something
    like (Defconst *eof-value* (cons nil nil)), (maybe it's eof-value, or
    si:eof-value, or sys:**eof-value**, I can never remember), so I can supply
    and test for it as an EOF-VALUE.   

    I would like to suggest the addition of new constant, *eof-value*, that
    is the default value for EOF-VALUE in all the read functions.  

    Every system using something like this, why not make it standard?

     - Kelly Murray
I second this proposal. Make EOF processing easy!