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[Axiom-developer] structural decomposition

From: daly
Subject: [Axiom-developer] structural decomposition
Date: Mon, 2 Apr 2007 13:52:35 -0500

The whole boot/shoe parser was a complete black box delivered whole
by Bill Burge so I don't know the details.

It looks like

['SEQ, :l, ['exit,1,x]] := item

tries to take a lisp s-expression and decompose it to extract
the "l", inner list construct. The axiom SEQ seems to expect
an (exit ....) s-expression as the last expression in the seq.

It may be that the convention changed and SEQ no longer required
the last s-expression to be an exit call but I don't know for sure.
The "1" might have been an error code? The s-expression this expects
seems to look like:

  (exit 1 x)

so maybe it was intended as an error code? If you can find the
runtime implementation of exit that might give you a clue.

You'll often see this kind of code (from SF.NRLIB/code.lsp)

(defun |DFLOAT;manexp (|x| $) (prog .....[snip]....
  (return (seq (exit (cond ((zerop |x| ...[snip]....


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