No unary '+' in 'POSIX bc'

I’m still trying to learn about computer languages, by targeting ‘POSIX bc’ to Parrot. Currently I’m checking whether I got the precedences of ’+’, ‘-‘, ’*’, ’/’ and ’%’ right. The harder things are still to come: variables and subroutines.

There is a funny thing I noticed about POSIX bc. POSIX bc has no unary ’+’, thus ‘+1’ on a line by itself is a syntax error.

bernhard@ubuntu:~$ bc -s
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type 'warranty'.
1
1
-1
-1
+1
(standard_in) 3: syntax error
0
0
quit
bernhard@ubuntu:~$