Re: Weird behavior of hash-table

[Mark H Weaver]

Hi Zelphir,

Zelphir Kaltstahl <address@hidden> writes:

> I've noticed a strange behavior of hash tables. I put in symbols as keys
> and integers as values, but when I try to get the integers out again by
> using the same symbol, I get back a #f instead. Here is the code I am using:
>
> ~~~~~~~~
> (use-modules
>  ;; SRFI 60: procedures for treating integers as bits
>  (srfi srfi-60)
>  (ice-9 hash-table))
>
>
> (define SQUARES
>   ;; vector, constant time access
>   #('A1 'B1 'C1 'D1 'E1 'F1 'G1 'H1
>     'A2 'B2 'C2 'D2 'E2 'F2 'G2 'H2
>     'A3 'B3 'C3 'D3 'E3 'F3 'G3 'H3
>     'A4 'B4 'C4 'D4 'E4 'F4 'G4 'H4
>     'A5 'B5 'C5 'D5 'E5 'F5 'G5 'H5
>     'A6 'B6 'C6 'D6 'E6 'F6 'G6 'H6
>     'A7 'B7 'C7 'D7 'E7 'F7 'G7 'H7
>     'A8 'B8 'C8 'D8 'E8 'F8 'G8 'H8))

I guess that you meant for this to be a vector of symbols.  In fact, it
is a vector of lists of the form (quote <symbol>), for which '<symbol>
is a shorthand.

  scheme@(guile-user)> (vector-ref SQUARES 0)
  $10 = (quote A1)

To fix the problem, remove all of the apostrophes (') from the elements
of the vector literal above.  Like list literals, vector literals take
raw values, not expressions.

> (hash-ref SQUARES-TO-INTEGERS 'A1)

  scheme@(guile-user)> (hash-ref SQUARES-TO-INTEGERS 'A1)
  $11 = #f
  scheme@(guile-user)> (hash-ref SQUARES-TO-INTEGERS ''A1)
  $12 = 1

       Mark