(*
BrainFuck Interpreter in SML 
© 2003 by Andreas Hartl
http://www.runicsoft.com
*)
                                                                                                                                                                                                  
fun BrainFuck file =
let
	val Buffer = Array.array ( 30000, 0 )
	val CodeBuffer = Array.fromList ( explode ( TextIO.inputAll ( TextIO.openIn ( file  ) ) ) )
	val ThePointer = ref 0
    	val InsPointer = ref 0
	val CurrentSymbol = ref #"0"
in
	while ( Array.length(CodeBuffer) > !InsPointer ) do
	(
		CurrentSymbol := Array.sub ( CodeBuffer, !InsPointer );
  
		case !CurrentSymbol of
		#">" => ThePointer := !ThePointer + 1
		| #"<" => ThePointer := !ThePointer - 1 
		| #"+" => Array.update ( Buffer, !ThePointer, Array.sub ( Buffer, !ThePointer ) + 1 )
		| #"-" => Array.update ( Buffer, !ThePointer, Array.sub ( Buffer, !ThePointer ) - 1 )
		| #"." => print ( Char.toString ( chr ( Array.sub ( Buffer, !ThePointer ) ) ) )
		| #"," => Array.update ( Buffer, !ThePointer, ord ( String.sub 
			( TextIO.inputN ( TextIO.stdIn, 1 ), 0 ) ) )
        		| #"[" => if Array.sub ( Buffer, !ThePointer ) = 0 then 
			let val looplevel = ref 1
                     		in 
                         			while !looplevel <> 0 do
                       			 (
                            				 InsPointer := !InsPointer + 1;
                           				 if Array.sub ( CodeBuffer, !InsPointer ) = #"["
			   		 then looplevel := !looplevel + 1
                           				 else if Array.sub ( CodeBuffer, !InsPointer ) = #"]"
                            				 then looplevel := !looplevel - 1
                            				 else looplevel := !looplevel	
                       			  )
		    	  end
                     		  else InsPointer := !InsPointer
        		| #"]" => let val looplevel = ref ~1
                		in 
                    		while !looplevel <> 0 do
                     		(
                          			InsPointer := !InsPointer - 1;
                          			if Array.sub ( CodeBuffer, !InsPointer ) = #"]"
			 	then looplevel := !looplevel - 1
                          			else if Array.sub ( CodeBuffer, !InsPointer ) = #"["
                          			then ( 
                               			if !looplevel = ~1 then (InsPointer := !InsPointer - 1;
                               			looplevel := !looplevel + 1)
				else looplevel := !looplevel + 1)
		         		 else looplevel := !looplevel
                  	   	 )
		   	end
        		| n => InsPointer := !InsPointer;         
      		InsPointer := !InsPointer + 1
     	)
end;