Function A($)
Dim $t,$x

For $t=0 to 15-($<4)
 $a=Right($,1)
 $x=$t mod 2 *(($a>4)+$a)+$a+$x
 $a=(2<$a & 7>$ & $x mod 10=)*$a
 $=Left($,~)
EndFunction

Function A($)
Dim $c, $t

	For $c=0 to 15-($<4)
		$A = 0 + right($, 1)
		$t = $c mod 2 * ($A / 5 + $A) + $A + $t
		$ = left($,~)
		If $t mod 10 + $ | 4&$A + 5
			$A = 0
Endfunction

; begin Luhns Mod
;
;!
Function A($)
Dim $c, $t

	For $c=0 to 15-($<4)
		$A = 0 + right($, 1)
		$t = $c mod 2 * ($A / 5 + $A) + $A + $t
		$ = left($,~)
		If $t mod 10 | 4&$A + 5
			$A = 0
Endfunction

;!
;!
; end Luhns Mod

Function A($D)
  Dim $,$F,$S				; Digit, Flag, ID, Sum
  $A=0
  $=Left($D,1)	;			; CC Issuer ID
  If ($D^)+($=3)=16 & $>2 & $<7 	; verify ID/# Digits
    While $D				; while digits
      $=Right($D,1)			; Get digit and optionally double
      $S=$S+$F*((4<$)+$)+$		; sum digit
      $F=$F^1				; flip odd/even flag
      $D=Left($D,~)			; trim string
      $A=($S Mod 10 =)*$		; if CC is valid
EndFunction

function a($)
    dim $b, $d
    while $
        $a = right($,1)
        $d = $d + (1&$b)*((4<$a)+$a)+$a
	$b=$b+1
        $a = ($d mod 10 =) * ($>2&$<7&$b+($<4)=16) * $
        $ = left($,~)
endfunction

Function A($)

	
	dim $i, $x, $b, $l
	$l = len($)

		redim $b[$l-1]
		for $i = 0 to $l-1
			$b[$i] = substr($,$i+1,1)
		next

		for $i = $l-2 to 0 step -2
			$x = 2*$b[$i]
			$b[$i] = iif($x>9,0+left($x,1) + right($x,1),$x)
		next

		$i = execute("$X="+join($b,'+'))

	$a = ($>3 & $<7 & $l=16-($<4) & $x mod 10=)*left($,1)

Function A($)	
	$a = $^0 ;no need for long keywords like len()
	dim $i, $x, $b[$a-1] ;$l removed using $a instead
	
		;redim $b[$a-1] ;no need to redim if doing right in the start ;)
		for $i = 0 to $a-1
			$b[$i] = substr($,$i+1,1)
		next

		for $i = $a-2 to 0 step -2
			$x = 2*$b[$i]
			$b[$i] = iif($x>9,0+left($x,1) + right($x,1),$x)
		next

		$i = execute("$X="+join($b,'+'))

	$a = ($>3 & $<7 & $a=16-($<4) & $x mod 10=)*left($,1)
Endfunction

Function A($)	
	$a = $^0 ;no need for long keywords like len()
	dim $i, $x, $b[$a-1] ;$l removed using $a instead
	
		;redim $b[$a-1] ;no need to redim if doing right in the start ;)
		for $i = 0 to $a-1
			$b[$i] = substr($,$i+1,1)
		next

		for $i = $a-2 to 0 step -2
			$x = 2*$b[$i]
			; $b[$i] = iif($x>9,0+left($x,1) + right($x,1),$x) redone without lettercode (right replaced with mod).
			;$b[$i] = iif($x>9,0+left($x,1) + $x mod 10,$x) x cannot be more than 18, so removing left(). also removing iif.
			$b[$i] = $x-9*($x>9)
		next

		$i = execute("$X="+join($b,'+'))

	$a = ($>3 & $<7 & $a=16-($<4) & $x mod 10=)*left($,1)
Endfunction

Function A($)	
	$a = $^0 ;no need for long keywords like len()
	dim $i, $x, $b[$a-1],$s ;$l removed using $a instead. $s introduced as "swinger"
	
		;redim $b[$a-1] ;no need to redim if doing right in the start ;)
		for $i = $a-1 to 0 step -1
			$x = substr($,$i+1,1)
			if $s ;second for loop removed. using swinger swapper instead.
				$x = 2*$x
				$x = $x-9*($x>9)
			endif
			$b[$i] = $x
			$s=$s^1
		next

		$i = execute("$X="+join($b,'+'))

	$a = ($>3 & $<7 & $a=16-($<4) & $x mod 10=)*left($,1)
Endfunction