Version 11 of Simple implementation of Real Number

Updated 2007-02-04 16:18:58

Suggested by Numerical Analysis in Tcl; how to implement numerical statements such as a=b*c. I have removed my own prodding code which has satisfactorily produced some good responses to show implementations that already exist such as Gadgets.

slebetman Notwithstanding the fact that a real number in mathematics means something completely different (see Computers and real numbers) I've implemented this concept a bit more intuitively (and if you consider lines of code, also more simply). Unlike the implementation (removed by original author), my variables exist as both variables and commands. Personally I would call it a C-like syntax for numbers:

GWM yes real numbers in maths are different but as this is a numerical analysis related item, real means whatever a compiled computer program uses as a real (especially the C language) - as used in numerical analysis. I agree that C-like syntax is a more appropriate term. I like this implementation by slebetman as it is simple, and allows local variables and recursion.

    proc cleanupVar {name1 name2 op} {
        rename $name1 {}
    }

    proc var {name {= =} args} {
        upvar 1 $name x
        if {[llength $args]} {
            set x [expr $args]
        } else {
            set x {}
        }
        proc $name args "
            upvar 1 $name $name
            if {\[llength \$args\]} {
                set $name \[expr \[lrange \$args 1 end\]\]
            } else {
                return \$[set name]
            }
        "
        uplevel 1 [list trace add variable $name unset cleanupVar]
    }

The following is an example of how to use var:

    proc test {} {
        var x
        var y = 10

        x = $y*2

        return $x
    }
    puts [test]

Another feature is that my variables actually exists in local scope even though their associated commands exists in global scope. This means that the variables can be used recursively:

    proc recursiveTest {x} {
        var y = $x - 1

        if {$y > 0} {
            recursiveTest $y
        }
        puts $y
    }
    recursiveTest 10

should output the numbers 0 to 9. Another test:

    proc test2 {} {
        var x = 10
        puts "this x belongs to test2 = $x"
    }

    proc test3 {} {
        var x = 100
        test2
        puts "this x belongs to test3 = $x"
    }

    test3

output:

  this x belongs to test2 = 10
  this x belongs to test3 = 100

Another, even more powerful, implementation of this concept is Let unknown know.

---

Category Core , Category Example , Category Mathematics