Implementing bool() without any conditionals

Question

Title says it all. Given some input, turn it into a boolean value (0 or 1), without using conditional statements (e.x. == > < <= >= != ~=), or any function which uses conditional statements within its implementation, such as if, while and for. Your program must work with floating points, although you get more if it works with other items.

A general rule for determining whether bool(item) is False is if the item is empty ('' is an empty string, [] is an empty list.), or if the function used to turn an item of one type into another is given no input (in Python, str() returns '', list() returns [].)

Here are (some of) the different valid types. Your program is considered to work with one type if it works with one item in the following lists:

• Integers, floating points, doubles, longs
• Strings
• Lists, tuples, arrays (bytearrays)
• Dictionaries
• Functions
• Objects/Classes

Program score will be calculated like this: [# of characters]-(50*[# of types]). The program with the smallest score wins the challenge.

Answer 1

Python - 122 chars - 50*13 types = -528

def b(x=False):
 try:return[False][x]
 except IndexError:return True
 except:
  try:return b(len(x))
  except:return True

Works for the following built-in types (as listed in §3.2 The standard type hierarchy)

1. NotImplemented
2. Ellipsis
3. int
4. long
5. bool
6. string
7. unicode
8. tuple
9. list
10. bytearray
11. set
12. frozenset
13. dict

Answer 2

JavaScript, -278

function bool(_,$){try{$=_.length;$._;_=$}catch(_){}return 1-isNaN(_/_)}

Doesn’t use any boolean operators! If global leaking and input is okay, then it’s even shorter, at 65 characters:

bool=eval.bind(0,'try{$=_.length;$._;_=$}catch(_){}1-isNaN(_/_)')

Works for anything with a length and all primitive types and their object wrappers.

Now you've added a list of things that count as types, but what kind of function or class should evaluate to false? This one treats functions that take no arguments as false - does that count? What about classes? What does that mean?

Answer 3

Scala(152 characters)

implicit def?(a:Any)={val f=false;a match{case 0=>f;case null=>f;case ""=>f;case ()=>f;case None=>f;case x:Iterable[_]=>x.exists(_=>true)case _=>true}}

Sample inputs:

scala> if(0) true else false
res0: Boolean = false

scala> if(0.0) true else false
res1: Boolean = false

scala> if(1) true else false
res2: Boolean = true

scala> if(()) true else false
res3: Boolean = false

scala> if(List()) true else false
res4: Boolean = false

scala> if(List(1)) true else false
res5: Boolean = true

scala> if(Set()) true else false
res6: Boolean = false

scala> if("") true else false
res7: Boolean = false

scala> if(Map()) true else false
res8: Boolean = false

scala> if(None) true else false
res9: Boolean = false

scala> class X
defined class X

scala> if(new X()) true else false
res10: Boolean = true

Answer 4

MMIX (8 bytes assembled)

Assembly language has no statements.

bool    ZSNZ $0,$0,1
        POP  1,0

Answer 5

GoRuby, 19 - 50*(number of types in Ruby)

def bool(o)
   [1,[o].fle.j.sz].mi
end

Returns 0 if the passed object converts to the empty string, 1 otherwise. Of course, Ruby doesn't treat 0 as false, so this isn't a very useful function...in fact, bool(bool(x)) is always 1. Objects that do convert to 0 include nil,false,[], and lists containing only objects that convert to 0.

Answer 6

Python 85 chars - 50*20 types = -915 points

def b(x=False):
 try:return b(len(x))
 except:return{0:False,None:False}.get(x,True)

So it works for all types in the six categories in the question. The score is therefore 85 - 50*6 = -215, or am I wrong?

Here is also my test code:

class Test(object):
  def __init__(self):
    pass

for x in [None, NotImplemented, Ellipsis, 
    0,1,0L,1L,False,True,0.0,1.0,0.0j,1.0j,
    '','a',u'',u'a',
    (),(1,),[],[1],bytearray(),bytearray('31'),
    set(),set('ab'),frozenset(),frozenset('ab'),
    {},{'a':0},b, Test, Test.__init__,(a for a in 'a')]:
  print b(x), bool(x), type(x)

Think I've forgotten some types ;-)

b(x) bool(x) type(x)
False False <type 'NoneType'>
True True <type 'NotImplementedType'>
True True <type 'ellipsis'>
False False <type 'int'>
True True <type 'int'>
False False <type 'long'>
True True <type 'long'>
False False <type 'bool'>
True True <type 'bool'>
False False <type 'float'>
True True <type 'float'>
False False <type 'complex'>
True True <type 'complex'>
False False <type 'str'>
True True <type 'str'>
False False <type 'unicode'>
True True <type 'unicode'>
False False <type 'tuple'>
True True <type 'tuple'>
False False <type 'list'>
True True <type 'list'>
False False <type 'bytearray'>
True True <type 'bytearray'>
False False <type 'set'>
True True <type 'set'>
False False <type 'frozenset'>
True True <type 'frozenset'>
False False <type 'dict'>
True True <type 'dict'>
True True <type 'function'>
True True <type 'type'>
True True <type 'instancemethod'>
True True <type 'generator'>

Answer 7

Perl, 5 char

1-!$x

Works for integers, floating-point values, strings, and C. Although in Perl, these are all the same type.