retroforth/doc/StackComments.md

Most words in RETRO have a stack comment. These look like:

(-)
(nn-n)

As with all comments, a stack comment begins with ( and should end with a ). There are two parts to the comment. On the left side of the - is what the word consumes. On the right is what it leaves.

RETRO uses a short notation, with one character per value taken or left. In general, the following symbols represent certain types of values.

b, n, m, o, x, y, z are generic numeric values           
s represents a string
v represents a variable
p, a represent pointers
q represents a quotation
d represents a dictionary header
f represents a `TRUE` or `FALSE` flag.

In the case of something like: (xyz-m) RETRO expects z to be on the top of the stack, with y below it and x below the y value. And after execution, a single value (m) will be left on the stack.

Words with no stack effect have a comment of (-)