## Saturday, November 22, 2008

### 99 problems - python - 48

Truth tables for logical expressions (3).

Generalize problem P47 in such a way that the logical expression may contain any number of logical variables. Define table/2 in a way that table(List,Expr) prints the truth table for the expression Expr, which contains the logical variables enumerated in List.

Example:
* (table (A,B,C) (A and (B or C) equ A and B or A and C))
true true true true
true true fail true
true fail true true
true fail fail true
fail true true true
fail true fail true
fail fail true true
fail fail fail true

def int_to_bool_tuple(x,size):
result = []
while x:
result.insert(0, (x & 1) == 1)
x >>= 1
return ([False]*(size-len(result))) + result

def table2(var_count, func):
for x in range(2**var_count):
bools = int_to_bool_tuple(x,var_count)
for b in bools:
print "%-5s" % b,
print func(*bools)

As I was exploring ideas for this solution I noticed that python 2.6 has a bin() function which gives a string representation of a number as binary. Need to upgrade to 2.6 I guess. Of course if I'm going to upgrade, might as well wait for 3.0.