Building a Select Case to call user functions

[kevin]

   Here's a #coding concept that's a little more for the advanced PlayBASIC coders to dip into. In this example (Bellow) were going to load some PlayBASIC source code; skim that code for function names that match a particular pattern, then output those function names to build a Select Code statement in source code.

 Why would we do this ?

  Well let's say you want to write simple scripts for your programs where the user can customize your programs behavior by feeding it a list of custom commands. There's all sort of levels to this, but often we just need something simple that will process an input string and call the functions required to perform the operations the user wants..

  Bellow we're focusing on the calling part of the this process, as often it's difficult to maintain part of building your own scripting parser as you have to write this code by hand; which is open to all that's errors. But we can avoid some of those problem by writing a program that will generate the code for us from our list of available functions.


  This PlayBASIC source code contains a function called "Build_Select_Statement" that takes a file name as an argument (in the form of a string). The function opens the file, reads its contents into a string, and closes the file. Then, the function searches for all instances of "function UCF_" in the string and stores each found function name in a list. The function then looks for a specific template function in the string, replaces the placeholder for the list of function names with the actual list, and outputs the modified template function.


 


   This example is a single file example of how you might generate a select case statement from a group of functions.    

   This PlayBASIC code contains a function called "Build_Select_Statement" that takes a file name as an argument (in the form of a string). The function opens the file, reads its contents into a string, and closes the file. Then, the function searches for all instances of "function UCF_" in the string and stores each found function name in a list. The function then looks for a specific template function in the string, replaces the placeholder for the list of function names with the actual list, and outputs the modified template function.

   
 

   NOTES:

          RUN IN DEBUG MODE =  F7 To Run
   
         You need to have saved this example for it run
        

PlayBASIC Code: [Select]

; PROJECT : User Callable Function Parser
; AUTHOR  : Kev Picone - PlayBASIC Tutor - Https://playbasic.com
; CREATED : 1/02/2023
; EDITED  : 1/02/2023
; ---------------------------------------------------------------------

   /*        
         RUN IN DEBUG MODE =  F7 To Run
   
         You need to have saved this example for it run
      
         In this example the generated code is output to the debug
         console, in a real world use case you would save it to disk
         and use the include directive to import the code into your
         project
         
   */   

   Build_Select_Statement("main.pba")


   Sync
   waitkey
   end   


Function Build_Select_Statement(File$)
   
      // You'd most like have a hand written template
      // but 
      fh=readnewfile(file$)
      if   fh
         RawCode$=readchr$(fh,Filesize(File$))      
         closefile fh         

         // End of line in TEXT file / Source code
         cr$=chr$(10)+Chr$(13)

         //  Find the functions that match out pattern
         Key$="function"+" UCF_"   

         // Insert the string that will hold our generated source code
         CaseCode$=cr$

         // Find the functions that match our key within this source code   
         LastMatch=0
         do
               MatchPos = instring(RAwCode$,key$,LastMatch,true)
               if MatchPos =0 then exitdo

               // Function the brackets after this 
               Open_Bracket_POs = instring(RawCode$,"(",MatchPos)
                
               if Open_Bracket_POs > MatchPOs

                     StartPos =MatchPos+Len(Key$)
                     Name$= mid$(RAwCode$,StartPOS,Open_Bracket_POs-StartPOS)   


                     // Make the SELECT CASE code to catch and call this function
                     CaseCode$   +="         case "+chr$(34)+upper$(Name$)+chr$(34)+cr$                     

                     //  Add the prefix to the name
                     Name$=replace$(Key$,"function ","")+Name$

                     CaseCode$   +="               "+Name$+"()"+cr$                     
                     CaseCode$   +=cr$                     
                  
               else
                     #print "Errror Missing after function name dude"
               endif   

               LastMatch = MatchPOs+Len(Key$)
         loop
      

         // -----------------------------------------------------------------
         //  Create the caller function from the template example
         // -----------------------------------------------------------------

         Pos =instring(RAwCode$,"Function"+" TEMPLATE_CALL_UCF_FUNCTION",0,1)
         if Pos>0
            EndPos =instring(RAwCode$,"//END OF TEMPLATE",pos,true)
            if EndPos>pos
               CustomFunction$    = mid$(RawCode$,Pos,EndPOS-pos)

               //  Remove the TEMPLATE from the function name               
               CustomFunction$ = replace$(CustomFunction$,"Function TEMPLATE_","Function ")

               // insert the CASES 
               CustomFunction$ = replace$(CustomFunction$,"//[INSERT CASES HERE]",CaseCode$)

               
               //  DUMP the Generate CODE TO THE DEBUG CONSOLE
               #print CustomFunction$



            endif
         endif
      endif   
   
EndFunction 



// -------------------------------------------------------------------
// -------------------------------------------------------------------
// -------------------------------------------------------------------
// -------------------------------------------------------------------

   
Function TEMPLATE_CALL_UCF_FUNCTION(Opcode$)
   
   Select upper$(OPcode$)      
   
         //[INSERT CASES HERE]   
   
   EndSelect
   
EndFunction
//END OF TEMPLATE





 // ----------------------------------------------------------------------
 // ----------------------------------------------------------------------
 // ----------------------->> FUNCTION LIBRARY <<-------------------------
 // ----------------------------------------------------------------------
 // ----------------------------------------------------------------------
 
function UCF_RedTEXT()
EndFunction

function UCF_GreenTEXT()
EndFunction

function UCF_BlueTEXT()
EndFunction

function UCF_CLS()
EndFunction

 Given an input file of the following PlayBASIC source code

Code Select Expand



// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
// ----------------------->> FUNCTION LIBRARY <<-------------------------
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------

function UCF_RedTEXT()
EndFunction

function UCF_GreenTEXT()
EndFunction

function UCF_BlueTEXT()
EndFunction

function UCF_CLS()
EndFunction








  This example creates

PlayBASIC Code: [Select]

// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
//  EXAMPLE OF THE CREATED CALLER FUNCTION
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
// ----------------------------------------------------------------------
   

Function CALL_UCF_FUNCTION(Opcode$)
   
   Select upper$(OPcode$)      
   
         

         case "REDTEXT"

               UCF_RedTEXT()


         case "GREENTEXT"

               UCF_GreenTEXT()


         case "BLUETEXT"

               UCF_BlueTEXT()


         case "CLS"

               UCF_CLS()


   
   
   EndSelect
   
EndFunction

   

Related PlayBASIC Source Code Examples

 - PlayBASIC (CLASSIC) Project Loader / Source Merger Functions

  - PLayBASIC Documentation: - See CallFunction