On Fri, Oct 17, 2014 at 07:44:27PM +0200, Michele La Monaca wrote:
> Hi,
>
> curiously:
>
>
> (cond (1 => odd?))
>
> Error: unbound variable: =>
>
> while
>
>
> (cond (+ => procedure?))
> #t
>
> The only difference I can spot is that 1 is self-evaluating while + is
> not. Anyhow, it doesn't look good to me.
Well-spotted! This was due to an optimisation which rewrote
(cond (CONSTANT <whatever> ...) ...) to <whatever>, which is correct,
but it forgot to rewrite (cond (CONSTANT => <whatever>) ...) to
(<whatever> CONSTANT).
The attached patch fixes it.
Thanks for reporting this issue!
Cheers,
Peter
--
http://www.more-magic.net
>From f66efec38cb6b7ebf34d70cfabafe9552807c9bd Mon Sep 17 00:00:00 2001
From: Peter Bex <peter....@xs4all.nl>
Date: Fri, 17 Oct 2014 20:46:15 +0200
Subject: [PATCH] Fix incorrect optimization in cond expansion.
When a constant is used as the condition, the consequence would be
simply taken as-is (or wrapped in a "begin" if it's multiple
statements). However, if there's a => following the constant, it should
expand to a call of the procedure with the constant as argument.
Reported by Michele La Monaca
---
NEWS | 2 ++
expand.scm | 9 ++++++---
tests/syntax-tests.scm | 5 +++++
3 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/NEWS b/NEWS
index 70b68fa..00b1475 100644
--- a/NEWS
+++ b/NEWS
@@ -49,6 +49,8 @@
- Syntax expander
- define-values, set!-values and letrec-values now support full lambda
lists as binding forms
+ - cond expands correctly when a constant is used in combination with =>
+ (thanks to Michele La Monaca)
- C API
- Removed deprecated C_get_argument[_2] and
diff --git a/expand.scm b/expand.scm
index 16a1370..966d4ba 100644
--- a/expand.scm
+++ b/expand.scm
@@ -1174,9 +1174,12 @@
(and (pair? (car clause))
(c (r 'quote) (caar clause))))
(expand rclauses (strip-syntax (car clause)))
- (if (null? (cdr clause))
- (car clause)
- `(##core#begin ,@(cdr clause))))
+ (cond ((and (fx= (length clause) 3)
+ (c %=> (cadr clause)))
+ `(,(caddr clause) ,(car clause)))
+ ((null? (cdr clause))
+ (car clause))
+ (else `(##core#begin ,@(cdr clause)))))
((null? (cdr clause))
`(,%or ,(car clause) ,(expand rclauses #f)))
((and (fx= (length clause) 3)
diff --git a/tests/syntax-tests.scm b/tests/syntax-tests.scm
index df0f607..ba9b3fc 100644
--- a/tests/syntax-tests.scm
+++ b/tests/syntax-tests.scm
@@ -196,6 +196,11 @@
(let ((baz 100))
(t "no baz" (kw baz)))
+;; Optimisation to rewrite constants with =>, reported by Michele La Monaca
+(t 2 (cond (1 2)))
+(f (cond (1 => string-length)))
+(t #t (cond (1 => odd?)))
+
(t 'ok
(let ((=> #f))
(cond (#t => 'ok)))
--
1.7.10.4
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