got rid of unsound co/contravariance in procvars

lib/pure/romans.nim

@@ -0,0 +1,59 @@
+#
+#
+#            Nimrod's Runtime Library
+#        (c) Copyright 2011 Philippe Lhoste
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## Module for converting an integer to a Roman numeral.
+## See http://en.wikipedia.org/wiki/Roman_numerals for reference.
+
+const
+  RomanNumeralDigits* = {'I', 'i', 'V', 'v', 'X', 'x', 'L', 'l', 'C', 'c', 
+    'D', 'd', 'M', 'm'} ## set of all characters a Roman numeral may consist of
+
+proc romanToDecimal*(romanVal: string): int =
+  ## Converts a Roman numeral to its int representation.
+  result = 0
+  var prevVal = 0
+  for i in countdown(romanVal.len - 1, 0):
+    var val = 0
+    case romanVal[i]
+    of 'I', 'i': val = 1
+    of 'V', 'v': val = 5
+    of 'X', 'x': val = 10
+    of 'L', 'l': val = 50
+    of 'C', 'c': val = 100
+    of 'D', 'd': val = 500
+    of 'M', 'm': val = 1000
+    else: 
+      raise newException(EInvalidValue, "invalid roman numeral: " & $romanVal)
+    if val >= prevVal:
+      inc(result, val)
+    else:
+      dec(result, val)
+    prevVal = val
+
+proc decimalToRoman*(number: range[1..3_999]): string =
+  ## Converts a number to a Roman numeral.
+  const romanComposites = [
+    ("M", 1000), ("CM", 900),
+    ("D", 500), ("CD", 400), ("C", 100),
+    ("XC", 90), ("L", 50), ("XL", 40), ("X", 10), ("IX", 9),
+    ("V", 5), ("IV", 4), ("I", 1)]
+  result = ""
+  var decVal = number
+  for key, val in items(romanComposites):
+    while decVal >= val:
+      dec(decVal, val)
+      result.add(key)
+
+when isMainModule:
+  import math
+  randomize()
+  for i in 1 .. 100:
+    var rnd = 1 + random(3990)
+    assert rnd == rnd.decimalToRoman.romanToDecimal
+