Boolean values: Difference between revisions

No objects in the standard library coerce to boolean, but user-written objects may choose to do so; they can then be used in place of booleans.

> to __conformTo(guard) {

> if (guard == boolean) { return true }

Erlang doesn't technically define boolean types. Instead, the atoms <tt>true</tt> and <tt>false</tt> are used. However, they are integrated well enough into the language there should be no problem with that as long as you don't expect false and true to mean anything but literal false and true.

true

2> 1 < 1.

false

3> 0 == false.

=={{header|FALSE}}==

=={{header|Forth}}==

In conditionals, zero is false, non-zero is true. There are predefined constants for the canonical forms (all bits set/clear).

=={{header|Haskell}}==

=={{header|Logo}}==

Logo has predefined symbols for true and false ("true and "false), which are the values returned by predicates and required by logical operators and conditionals.

print 1 > 0 ; true

if "true [print "yes] ; yes

Unlike other lispy languages, there are no other implicit conversions. You must test explicitly for zero or empty collections.

if empty? [] [print "empty] ; empty list

=={{header|Metafont}}==

False

>>> bool("False")

=={{header|R}}==

=={{header|SNUSP}}==

Zero is false and non-zero is true, as used by the sole skip-if-zero operator ('''?''').

=={{header|Standard ML}}==

VB has the <code>Boolean</code> data type and the constants <code>True</code> and <code>False</code>, in addition to what's listed under [[#BASIC|BASIC]], above. When used outside of a boolean context, <code>True</code> and <code>False</code> return values depending on their context -- <code>-1</code> and <code>0</code> in a numeric context, <code>"True"</code> and <code>"False"</code> if used as strings.

x = IIf(Int(Rnd * 2), True, False)

MsgBox x</lang>

=={{header|XSLT}}==