Version 5 of A Money Package

Updated 2008-07-04 09:06:17 by jmn

George Peter Staplin July 3 2008 -- Here is a simple package for handling money without floating point. It may not be ideal for everyone -- yet. Feel free to improve this, and extend this page.

It could probably use a money-precision command for setting the precision of the numbers after the decimal point.

JMN This might be a nice start for the API - but as it stands it's wildly inaccurate.

e.g calculate 10% tax on 12.42

 %package require money
 1.0
 %money-value [money/ [money 19.11] 10]
 1.1

The point of a money package should not be so much to avoid floating-point operations at all cost - but to operate at a level where the errors are at a minimum and you choose when and with what method you do your rounding. e.g by using cents or even some fraction of a cent as your basic unit for calculation and storage.

Other languages seem to have pushed towards a Decimal datatype for currency work.

Martyn Smith My simple solution was to do all math using integer cents/centimes values and just to display a ./, in the right place when displaying any values, the integer math is very quick and no rounding problems.


 #By George Peter Staplin
 #Use it, share it, modify it, don't blame me.

 package provide money 1.0

 proc money value {
         lassign [split $value .] dol cents

         set dol [expr {$dol + ($cents / 100)}]
         set cents [expr {$cents % 100}]
         list $dol $cents        
 }

 proc money-value m {
         join $m .
 }

 proc money-pretty m {
         return \$[join $m .]
 }

 proc money+ {a b} {
         lassign $a adol acent
         lassign $b bdol bcent

         set dollars [expr {$adol + $bdol}]
         set cents [expr {$acent + $bcent}]
         set dollars [expr {$dollars + ($cents / 100)}]
         set cents [expr {$cents % 100}]
         list $dollars $cents
 }

 proc money- {a b} {
         lassign $a adol acents
         lassign $b bdol bcents

         set cents [expr {$acents - $bcents}]
          if {$cents < 0} {
                 incr adol -1
                 set cents [expr {$cents + 100}]
         }
         set dollars [expr {$adol - $bdol}]
         list $dollars $cents                
 }

 proc money* {a integer} {
         lassign $a adol acent

         set dollars [expr {$adol * $integer}]
         set cents [expr {($acent * $integer)}]
         set dollars [expr {$dollars + ($cents / 100)}]
         set cents [expr {$cents % 100}]
         list $dollars $cents
 }

 proc money/ {a integer} {
         lassign $a adol acent
         set cents [expr {$acent / $integer}]
         set dollars [expr {$adol / $integer}]
         list $dollars $cents
 }

 set cd [money 12.45]
 set car [money 3999.99]

 puts "CD + CAR [money-value [money+ $cd $car]]"

 puts [money-value [money* [money+ $cd $car] 2]]

 puts "44.02 - 12.99: [money-value [money- [money 44.02] [money 12.99]]]"

 puts "42.0 / 4: [money-value [money/ [money 42.0] 4]]"

 puts "45.5 / 3: [money-value [money/ [money 45.5] 3]]"

 puts "42.0 * 42 * 42 = You're rich! = [money-pretty [money* [money* [money 42.0] 42] 42]]"

Category Currency and Finance