1. # Code from http://sandbox.mc.edu/~bennet/ruby/code/poly_rb.html
2. #
3. # This program evaluates polynomials.  It first asks for the coefficients
4. # of a polynomial, which must be entered on one line, highest-order first.
5. # It then requests values of x and will compute the value of the poly for
6. # each x.  It will repeatly ask for x values, unless you the user enters
7. # a blank line.  It that case, it will ask for another polynomial.  If the
8. # user types quit for either input, the program immediately exits.
9. #
10.  
11. #
12. # Function to evaluate a polynomial at x.  The polynomial is given
13. # as a list of coefficients, from the greatest to the least.
14. def polyval(x, coef)
15.     sum = 0
16.     coef = coef.clone           # Don't want to destroy the original
17.     while true
18.         sum += coef.shift       # Add and remove the next coef
19.         break if coef.empty?    # If no more, done entirely.
20.         sum *= x                # This happens the right number of times.
21.     end
22.     return sum
23. end
24.  
25. #
26. # Function to read a line containing a list of integers and return
27. # them as an array of integers.  If the string conversion fails, it
28. # throws TypeError.  If the input line is the word 'quit', then it
29. # converts it to an end-of-file exception
30. def readints(prompt)
31.     # Read a line
32.     print prompt
33.     line = readline.chomp
34.     raise EOFError.new if line == 'quit' # You can also use a real EOF.
35.            
36.     # Go through each item on the line, converting each one and adding it
37.     # to retval.
38.     retval = [ ]
39.     for str in line.split(/\s+/)
40.         if str =~ /^\-?\d+$/
41.             retval.push(str.to_i)
42.         else
43.             raise TypeError.new
44.         end
45.     end
46.  
47.     return retval
48. end
49.  
50. #
51. # Take a coeff and an exponent and return the string representation, ignoring
52. # the sign of the coefficient.
53. def term_to_str(coef, exp)
54.     ret = ""
55.  
56.     # Show coeff, unless it's 1 or at the right
57.     coef = coef.abs
58.     ret = coef.to_s     unless coef == 1 && exp > 0
59.     ret += "x" if exp > 0                               # x if exponent not 0
60.     ret += "^" + exp.to_s if exp > 1                    # ^exponent, if > 1.
61.  
62.     return ret
63. end
64.  
65. #
66. # Create a string of the polynomial in sort-of-readable form.
67. def polystr(p)
68.     # Get the exponent of first coefficient, plus 1.
69.     exp = p.length
70.  
71.     # Assign exponents to each term, making pairs of coeff and exponent,
72.     # Then get rid of the zero terms.
73.     p = (p.map { |c| exp -= 1; [ c, exp ] }).select { |p| p[0] != 0 }
74.  
75.     # If there's nothing left, it's a zero
76.     return "0" if p.empty?
77.  
78.     # *** Now p is a non-empty list of [ coef, exponent ] pairs. ***
79.  
80.     # Convert the first term, preceded by a "-" if it's negative.
81.     result = (if p[0][0] < 0 then "-" else "" end) + term_to_str(*p[0])
82.  
83.     # Convert the rest of the terms, in each case adding the appropriate
84.     # + or - separating them.  
85.     for term in p[1...p.length]
86.         # Add the separator then the rep. of the term.
87.         result += (if term[0] < 0 then " - " else " + " end) +
88.                 term_to_str(*term)
89.     end
90.  
91.     return result
92. end
93.        
94. #
95. # Run until some kind of endfile.
96. begin
97.     # Repeat until an exception or quit gets us out.
98.     while true
99.         # Read a poly until it works.  An EOF will except out of the
100.         # program.
101.         print "\n"
102.         begin
103.             poly = readints("Enter a polynomial coefficients: ")
104.         rescue TypeError
105.             print "Try again.\n"
106.             retry
107.         end
108.         break if poly.empty?
109.  
110.         # Read and evaluate x values until the user types a blank line.
111.         # Again, an EOF will except out of the pgm.
112.         while true
113.             # Request an integer.
114.             print "Enter x value or blank line: "
115.             x = readline.chomp
116.             break if x == ''
117.             raise EOFError.new if x == 'quit'
118.  
119.             # If it looks bad, let's try again.
120.             if x !~ /^\-?\d+$/
121.                 print "That doesn't look like an integer.  Please try again.\n"
122.                 next
123.             end
124.  
125.             # Convert to an integer and print the result.
126.             x = x.to_i
127.             print "p(x) = ", polystr(poly), "\n"
128.             print "p(", x, ") = ", polyval(x, poly), "\n"
129.         end
130.     end
131. rescue EOFError
132.     print "\n=== EOF ===\n"
133. rescue Interrupt, SignalException
134.     print "\n=== Interrupted ===\n"
135. else
136.     print "--- Bye ---\n"
137. end
138.