var.eval.fmfn

/*
 * =====================================================
 * var.eval( contents )
 * 
 * RETURNS:        (bool) True or False based on proper evaluation
 * DEPENDENCIES:   none 
 * NOTES:          Try to always use the List() function when passing multiple values into var.eval!
 *                 $checkScriptName is a reserved local variable used when you wish to enforce
 *                 that inbound parameters match the name of the script. It is reset after the
 *                 evaluation.
 * RELEASE:        100909
 * =====================================================
 * 
 * This custom function evaluates contents passed as the
 * variable declaration part of a Let function. Useful for
 * defining global or locally scoped variables.
 * 
 */

 Let( [
   $$ERROR.VAR.EVAL = ""; // Reset global error variable for evaluation

   var.empty = IsEmpty ( contents ); // test for empty contents
   var.semicolons_exist = ( ValueCount ( contents ) = PatternCount ( contents ; ";¶" ) ) or ( ValueCount ( contents ) - 1 = PatternCount ( contents ; ";¶" ) );
   var.contents = If ( not var.semicolons_exist ; Substitute ( contents ; ¶ ; ";¶") ; contents ); // Add semicolons if needed
   var.trailing_semicolon = Right ( var.contents ; 1 ) = ";"; // Clean off the trailing semicolon if present
   var.contents = If ( var.trailing_semicolon; Left ( var.contents ; Length( var.contents ) - 1 ); var.contents );

   var.script = Get ( ScriptName );
   var.begin  = "(" ; // beginning of parameters definition
   var.break  = "," ; // regular parameters separator (and)
   var.end    = ")" ; // end of parameters definition

   var.parameters = Middle ( var.script ;
                      Position ( var.script ; var.begin ; 1 ; 1 ) +1;
                      Position ( var.script ; var.end ; Length ( var.script ) ; -1 ) - Position ( var.script ; var.begin ; 1 ; 1 ) -1
                   ); // raw parameters
   // ONLY ALLOWED CHARACTERS FOR SCRIPT NAME PARAMERS ARE THE FOLLOWING (minus the ¶)
   var.parameters = Filter ( Substitute ( var.parameters ; var.break ; ¶ ) ; "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_¶" );
   var.expected = "$" & Substitute ( var.parameters ; ¶ ; "¶$" );
   var.matching = FilterValues ( Substitute( var.contents; "="; ¶ ) ; var.expected ); // matching parameters found in ScriptName
   var.matching = If ( Right ( var.matching; 1 ) = "¶" ; Left ( var.matching ; Length ( var.matching) - 1) ); // replace extra return added by FilterValues function
   var.missingParams = If ( $checkScriptName = True ; var.matching ≠ var.expected ; False )
 ];

   If ( Evaluate( "Let ( [" & var.contents & "]; False )" ) = "?" // generates an error or
        or var.empty or var.missingParams; // empty contents or missing expected parameters
       // Return error result
       Let ( [
         $$ERROR.VAR.EVAL =
         Case (
           var.empty ; "EMPTY PARAMETER SET" ;
           var.missingParams ; "MISSING EXPECTED PARAMETERS PER SCRIPT NAME";
           List ( "ERROR »"; var.contents )
         );
         $checkScriptName = "" // reset the $checkScriptName variable (after setting error)
         ];
         False
       );
       Let ( $checkScriptName = "" ; True )
   )

 )