From: Steven Hansen <runner@...>
Date: 2006-09-05T11:59:42+09:00
Subject: Binary Search Using Lambda


Greetings,

I've been playing around with various ways to write a function that  
does a binary search on an array of integers.
Below is one of my implementations.  I'm wondering if it is possible  
to avoid passing the function to itself
in order to achieve the recursive call.  While I'm defining the  
function's body, is there a special syntax to define
a recursive call to the function being defined?

I'm also interested in any feedback folks may have to offer regarding  
the below implementation.

Thanks,
Steven



# Attempts to locate "int" in "int_array"
# if "int" is found, this function will return
# the index of "int's" location.  If "int" is not
# found, this function will return -1. This function
# assumes that "int_array" is already sorted in
# ascending order.
#
# Example: chop(3, [1, 2, 3, 4, 5]) #=> 2

def chop(int, int_array)
   func = lambda { |low, high, int, int_array, f|
     return -1 if high < low
     mid = low + ((high-low) / 2)

     if int < int_array[mid]
       high = mid-1
     elsif int > int_array[mid]
       low = mid+1
     else
       return mid
     end

     f.call(low, high, int, int_array, f)
   }

   func.call(0, int_array.size-1, int, int_array, func)
end