I had the same problem and managed to solve it as follows: fsharpi is a shell script; it does not work on line 24:
$EXEC mono $DEBUG $MONO_OPTIONS /Library/Frameworks/Mono.framework/Versions/4.0.4/lib/mono/4.5/fsi.exe --exename:$(basename "$0") "$@"
-, Xamarin fsharpi, , , , $PATH , fsharpi .
mac "/Library/Frameworks/Mono.framework/Commands/mono", :
MONO="/Library/Frameworks/Mono.framework/Commands/mono"
$EXEC $MONO $DEBUG $MONO_OPTIONS /Library/Frameworks/Mono.framework/Versions/4.0.4/lib/mono/4.5/fsi.exe --exename:$(basename "$0") "$@"
, script fsi.exe, .