psuedo code - not proper MMBasic but just read the manual

open COM1 as output #1
open midifile for input as #2
while not end of input file
get byte from midifile
send byte out COM1
loop

f$=" test "+chr$(9)+" "
print "*";f$;"*"
print "*";rtrim$(f$);"*"
print "*";ltrim$(f$);"*"
'F$=ltrim$(f$)
print "*";rtrim$(ltrim$(f$));"*"


FUNCTION LTrim$(a$)
LOCAL n
if len(a$)=0 then
LTrim$ = ""
else
FOR n= 1 TO LEN(a$)
IF MID$(a$,n,1)<>" " and MID$(a$,n,1)<>CHR$(9) THEN exit for
NEXT n
LTrim$=mid$(a$,n)
endif
END FUNCTION

FUNCTION RTrim$(a$)
LOCAL n
if len(a$)=0 then
RTrim$ = ""
else
FOR n= LEN(a$) TO 1 step -1
IF MID$(a$,n,1)<>" " and MID$(a$,n,1)<>CHR$(9) THEN exit for
NEXT n
RTrim$=left$(a$,n)
endif
END FUNCTION

F$=ltrim$(f$)
print "*";rtrim$(F$);"*"

print 99999 + 0.1
print 100000 + 0.1
print 100001 - 0.1
print 99999 - 0.1

OUTPUT:

99999.1
100000
100001
99998.9