2019-03-18 15:52:49 +01:00
|
|
|
# Stack Diagrams
|
|
|
|
|
|
|
|
|
|
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 (-)
|
