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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 (-)