(let ((i 0)(Beat1 #f) (Beat2 #f) (LilyString #f) (DisplayString #f) (Input #f) (NewBPM 100) (ValidBPM? #f)(MidiBPM 100) )

;GetBPM:
;sets MidiBPM, ValidBPM? based on user input.  This will allow denemo's midi to respect the beat change.
(define (GetBPM BaseBeat )  	
	(let ((dotted #f)(defaultBPM "60") (len 1)(duration 1)(bpm 60))
		
		;if BaseBeat is not specified, must query the user as to what should be the first beat unit:
		(if (equal? "" BaseBeat)  (set! BaseBeat (d-GetUserInput (_ "Metronome Marking") (_ "Give unit beat duration (e.g., 4. for dotted-quarter) \n or enter n for none:") "4" )))
		
		(if (or (equal? BaseBeat (_ "n") ) (equal? #f BaseBeat))
		
			;if user doesn't want to use BPM.
			(set! ValidBPM? #f)	
			
			; if user wants to use bpm...
			(begin 				
				(set! len (string-length BaseBeat) ) 
				(set! dotted (equal? "." (substring BaseBeat (- len 1) len ))  ) ;see if a dot at end
				(if dotted
					(set! duration (substring BaseBeat 0 (- len 1)))  ;if there's a dot, cut it off from BaseBeat to get base duration.
					(set! duration BaseBeat)  
				)			
				
				(set! bpm (d-GetUserInput (_ "Metronome Marking")  (string-append (_ "Give number of these ") BaseBeat (_ " beats per minute:")) defaultBPM ) )
				
				
				(set! ValidBPM?   (not (equal? (and (string->number duration) (string->number bpm) ) #f)))  ;don't go unless both are numbers.
				
				;don't go unless base duration is valid lilypond: (could go higher if wanted):
				(set! ValidBPM? (and ValidBPM? (or   (equal? duration "1")(equal? duration "2")(equal? duration "4")(equal? duration "8")
					(equal? duration "16")) ) )
				(if (and bpm  (equal? ValidBPM? #t))
					(if dotted (set! MidiBPM (number->string (floor (* (/ (string->number bpm) (string->number duration)) 6 ) ) ) ) 
						(set! MidiBPM (number->string (floor (* (/ (string->number bpm) (string->number duration) ) 4))  ) )
					) ;want * 3/2 for dotted,*4 since midi uses quarters and divide by duration,     
					(d-WarningDialog "Incorrect BPM syntax.")
				)
			)
		)
	);let
	);define GetBPM
	
	;Begin of main function
	
	;Input from the user what kind of beat change they want:
	(set! Input (d-GetUserInput (_ "Beat Change") 
		(string-append (_ "Enter beat change as [beat1]=[beat2] with the beats in Lilypond syntax,")
		(_ "\ni.e. 4 for quarter, 4. for dotted quarter, etc.")
		(_ "\nPlace immediately after a barline to center the beat change  over the barline."))
	 "4=4."))
	 
	;remove spaces from Input:		
	(set! DisplayString Input)
	(set! i (string-index Input #\=))
	(set! Beat1 (substring Input 0 i))
	(set! Beat2 (substring Input (+ 1 i)))
	
	;now we want to get the new bpm from the user.  Because e.g., if we had 4=100, and now 4. is the beat, we want the midi to be at a bpm of 4=150.  
	;This could be done automatically by a smart script that learned the current BPM and modified it appropriately.
	(set! MidiBPM (GetBPM Beat2))
	
	;set the string that tells lilypond how to make a beat change:
	(set! LilyString (string-append "\\mark \\markup \\tiny { \\general-align #Y #DOWN \\note #\"" Beat1 "\" #UP = \\general-align #Y #DOWN \\note #\"" Beat2 "\" #UP } "))
			
	;now put in all the info into the denemo directive, including a midi bpm change if we have a valid one:
	(d-DirectivePut-standalone "BeatChange")
	(d-DirectivePut-standalone-postfix "BeatChange" LilyString)
	(d-DirectivePut-standalone-display "BeatChange" DisplayString)
	(d-DirectivePut-standalone-minpixels "BeatChange" 15)
	(if (equal? ValidBPM? #t)
		(begin 
			(d-DirectivePut-standalone-override "BeatChange" (logior DENEMO_OVERRIDE_TAGEDIT DENEMO_OVERRIDE_TEMPO DENEMO_OVERRIDE_STEP))
			(d-DirectivePut-standalone-midibytes "BeatChange" MidiBPM)
		)
	)
	(d-RefreshDisplay)		
)