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I am trying to learn Common Lisp with the book Common Lisp: A gentle introduction to Symbolic Computation. In addition, I am using SBCL, Emacs, and Slime.

In chapter 14, the last one, the author covers macros. He presents a tool called PPMX which stands for: ‘‘Pretty Print Macro eXpansion’’.

With this tool, you can do:

> (ppmx (incf a))
Macro expansion:
(SETQ A (+ A 1))

The tool is self-contained since the book provides the code definition for it:

(defmacro ppmx (form)
  "Pretty prints the macro expansion of FORM."
  ‘(let* ((exp1 (macroexpand-1 ’,form))
          (exp (macroexpand exp1))
          (*print-circle* nil))
     (cond ((equal exp exp1)
            (format t "~&Macro expansion:")
            (pprint exp))
           (t (format t "~&First step of expansion:")
              (pprint exp1)
              (format t "~%~%Final expansion:")
              (pprint exp)))
     (format t "~%~%")
     (values)))

Unfortunately, I cannot run it because the compilation does not work. The Slime's REPL throws this error:

ch-14.lisp:3:33:
  read-error: 
    READ error during COMPILE-FILE:
    
      Comma not inside a backquote.
    
        Line: 3, Column: 33, File-Position: 101
    
        Stream: #<SB-INT:FORM-TRACKING-STREAM for "file /tmp/slimeD4xBr3" {10036BFC63}>

Compilation failed.

The comma and left single quote look different in emacs than in SO: enter image description here

I have had some problems when copying the code from the book to emacs. It was basically inserting ' instead of the left single quote.

1 - Is there a way to fix this?

2 - The book was written in the late 1980s. Thus, I bet there are better tools now. Does Slime or SBCL offer some command to pretty print macro expansions? Maybe a library or another package?

Thanks.

Pᴇʜ
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Pedro Delfino
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    You're using a curly quote `‘`, not an ASCII backquote `\` ` – Barmar Aug 18 '21 at 22:12
  • Thanks! But, even fixing that, the REPL still indicates: `The variable FORM is unbound. [Condition of type UNBOUND-VARIABLE]` – Pedro Delfino Aug 18 '21 at 23:16
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    You also have a curly quote here: `’,form`. That should be an ASCII single quote `'` – Barmar Aug 18 '21 at 23:19
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    Use a programming editor or turn off "smart quotes" when editing code. – Barmar Aug 18 '21 at 23:19
  • Ok, thanks. I am using Emacs, I will check how to do it in Emacs. The REPL is returning `(ppmx (setf a 1)) Macro expansion: FORM` which is quite different from the book. @Barmar, do you suggest any tool to pretty print the macro? Or a command in SBCL or Slime? – Pedro Delfino Aug 18 '21 at 23:25
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    If you just do `(setq *print-pretty* t)` before `(macroexpand '(...))` it will pretty-print it in the REPL. – Barmar Aug 18 '21 at 23:27
  • Ok, perfect. It works. Thank you! – Pedro Delfino Aug 18 '21 at 23:29

1 Answers1

1

Following @barmar's advice, the user just need to write in the REPL:

CL-USER> *print-pretty*
T
CL-USER> (macroexpand (setf a 1))  ;without the quote it does not work
1
NIL
CL-USER> (macroexpand '(setf a 1)) ;with the quote it does
(SETQ A 1)
T
Pedro Delfino
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