41 lines
1.4 KiB
Text
41 lines
1.4 KiB
Text
# Stack Diagrams
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Most words in RETRO have a stack comment. These look like:
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(-)
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(nn-n)
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As with all comments, a stack comment begins with `(` and
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should end with a `)`. There are two parts to the comment.
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On the left side of the `-` is what the word *consumes*. On
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the right is what it *leaves*.
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RETRO uses a short notation, with one character per value
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taken or left. In general, the following symbols represent
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certain types of values.
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| Notation | Represents |
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| ------------------- | ----------------------- |
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| b, n, m, o, x, y, z | generic numeric values |
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| s | string |
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| v | variable |
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| p, a | pointers |
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| q | quotation |
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| d | dictionary header |
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| f | `TRUE` or `FALSE` flag. |
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In the case of something like `(xyz-m)`, RETRO expects z to be
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on the top of the stack, with y below it and x below the y
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value. And after execution, a single value (m) will be left on
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the stack.
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Words with no stack effect have a comment of (-)
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For combinators (words consuming quotations), you can include
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a sub-comment indicating the expected stack effect of the
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quote. E.g.,
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(q(-f)-)
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Indicates a word consuming a quote and returning nothing. The
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quote should return a flag.
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