bug#16238: 24.3.50; pcase docs (and possibly pcase) wrong

[Tassilo Horn]

I'm just reading through the `pcase' docs in the info manual.  The
simple expression language example has a small bug.  The `env' parameter
is missing at the location marked below:

--8<---------------cut here---------------start------------->8---
(defun evaluate (exp env)
  (pcase exp
    (`(add ,x ,y)         (+ (evaluate x env) (evaluate y env)))
    (`(call ,fun ,arg)    (funcall (evaluate fun) (evaluate arg env)))
                                                `--- HERE!
    (`(fn ,arg ,body)     (lambda (val)
                            (evaluate body (cons (cons arg val) env))))
    ((pred numberp)       exp)
    ((pred symbolp)       (cdr (assq exp env)))
    (_                    (error "Unknown expression %S" exp))))
--8<---------------cut here---------------end--------------->8---

But even then, I can't get `fn' forms working:

ELISP> (evaluate '(fn x (add 1 x)) nil)
(lambda
  (val)
  (evaluate body
            (cons
             (cons arg val)
             env)))

But shouldn't `arg' be substituted with 'x and `body' with '(add 1 x)?
Now when I call the function, I get a void-variable error whereas I
should get 3:

ELISP> (evaluate '(call (fn x (add 1 x)) 2) nil)
*** Eval error ***  Symbol's value as variable is void: body

Strange enough, the `call' pattern which uses the same pattern syntax
seems to work, though:

ELISP> (evaluate '(call foo 2) '((foo . (lambda (x) (+ 1 x)))))
3 (#o3, #x3, ?\C-c)

In any case, it would be good if the docs would contain a sample program
defined in the simple expression language.  Getting the syntax right
just from the patterns is not enough.  For example, it's not obvious
that `fn' forms take only one symbol as `arg' whereas you'd usually
expect an argument list (which might be restricted to length 1).



In GNU Emacs 24.3.50.2 (x86_64-pc-linux-gnu, GTK+ Version 3.8.7)
 of 2013-12-22 on thinkpad
Bzr revision: eliz@gnu.org-20131222183138-zlzn9zzpz1hwd110
Windowing system distributor `The X.Org Foundation', version 11.0.11499904
System Description:     NAME=Gentoo

Configured using:
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Important settings:
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