[pmoriarty]

In guile[1]:

  % guile
  guile> (= (+ 0.1 0.2) 0.3)
  #f

[1] - https://www.gnu.org/software/guile/

[jgrant27]

Guile(and most Lisps such as Common Lisp) support rationals specifically to avoid this problem, why not just use them ?

  scheme@(guile-user)> (= (+ 1/10 2/10) 3/10)
  $1 = #t

[draegtun]

perl6 also use rationals (by default)...

  $ perl6

  > 0.1 + 0.2 == 0.3
  True

  > (0.1 + 0.2).perl
  3/10

For perl5 you must use the bigrat pragma:

  $ re.pl

  > 0.1 + 0.2 != 0.3
  1

  > use bigrat;
  > 0.1 + 0.2 == 0.3
  1

ref: http://perldoc.perl.org/bigrat.html

[pmoriarty]

"why not just use them ?"

Sometimes decimal notation is the most natural, and sometimes you're copying numbers in decimal notation out of a book, wikipedia, or some other publication.