Programming Praxis

Over at his blog, where he has been solving the exercises in SICP, Bill Cruise reached the section of the book that discusses interval arithmetic; if you want an introduction to the topic, you might want to look at http://www.cs.utep.edu/interval-comp/hayes.pdf.

Given an interval [x,y] with x the lower bound and y the upper bound, the basic operations of interval arithmetic are defined as follows:

• [a,b] + [c,d] = [a+c,b+d]
• [a,b] − [c,d] = [a−d,b−c]
• [a,b] × [c,d] = [min(ac,ad,bc,bd), max(ac,ad,bc,bd)]
• [a,b] ÷ [c,d] = [min(a/c,a/d,b/c,b/d), max(a/c,a/d,b/c,b/d)], where division by an interval containing zero is undefined

Your task is to write a basic library for interval arithmetic; you may do as many of the SICP exercises as you wish. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

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