Re: Weird behavior of hash-table

[Mark H Weaver]

Hi tomás,

<address@hidden> wrote:

> So the best thing for one's brain is to train it to read #(...)
> as some weird relative of '(...)?

Yes.  They are both literals, and no part of a literal is evaluated.
#(...) is actually a shorthand for '#(...), and incidentally, one which
was not standardized until the R7RS.  In portable R[3456]RS code, you
must explicitly quote vector literals.

It's important to distinguish between an expression and the value(s) it
evaluates to.  It's easy to confuse them in Scheme, where every
expression is a value, but not necessarily the same value that it
evaluates to.  For example, the expression (+ 1 1) is a list of length 3
which evaluates to the number 2.  Similarly, 'A1, which is a shorthand
for (quote A1), is a list of two symbols which evaluates to the symbol
A1.  Only the "self-evaluating" values evaluate to themselves.

In general, you should not put a quote (') anywhere that you could not
write (+ 1 1) in place of 2, unless of course you *want* a list starting
with the symbol 'quote'.

> Is there a corresponding weird relative of `(...)?

Yes.  Remember that #(...) is a shorthand for '#(...).  You can replace
the "'" with "`", just as you would for a quasiquoted list.  For
example:

  scheme@(guile-user)> `#(1 2 3)
  $1 = #(1 2 3)
  scheme@(guile-user)> `#(1 ,(+ 1 1) 3)
  $2 = #(1 2 3)
  scheme@(guile-user)> `#(1 (+ 1 1) 3)
  $3 = #(1 (+ 1 1) 3)

      Regards,
        Mark