Inconsistent 'return value' for definitions

[Mark H Weaver <mhw@netris.org>]

Hello all,

I think the following behavior is inconsistent and undesirable:

  scheme@(guile-user)> (list (compile '(define foo 3)))
  $1 = (#<unspecified>)
  scheme@(guile-user)> (list (primitive-eval '(define foo 3)))
  $2 = (#<variable 103b9c80 value: 3>)

It doesn't really make sense for 'define' to return a value, because it
cannot be used in expression context.  AFAICT, the only way to get this
'return value' is to call 'eval' or 'primitive-eval'.  This weirdness
has bitten Paul Smith in his efforts to port his code to Guile 2.

I think we should change 'define' to always "return" SCM_UNSPECIFIED, at
least in 2.2.  We might also consider nipping this in the bud and making
the same change in 2.0.4.

    Thanks,
      Mark