[Chicken-hackers] [PATCH] Allow "unsetting" read syntax

[Felix]

This patch allows removing read-syntax installed with "set-read-syntax!"
and related procedures. 

Fixes bug #940.


cheers,
felix

>From 08980cda014d51f3d06e5adc18d19f51f4bf5fb1 Mon Sep 17 00:00:00 2001
From: felix <address@hidden>
Date: Sun, 28 Oct 2012 13:47:20 +0100
Subject: [PATCH] allow unsetting read-syntax

---
 library.scm         |    8 ++++++--
 manual/Unit library |    4 ++++
 types.db            |   11 ++++++++---
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/library.scm b/library.scm
index 680687f..f884591 100644
--- a/library.scm
+++ b/library.scm
@@ -3065,9 +3065,13 @@ EOF
             (unless (##sys#slot crt slot)
               (##sys#setslot crt slot (##sys#make-vector 256 #f)) )
             (##sys#check-char chr loc)
-            (let ([i (char->integer chr)])
+            (let ((i (char->integer chr)))
               (##sys#check-range i 0 256 loc)
-              (##sys#setslot (##sys#slot crt slot) i (wrap proc)) ) ) ) ) )
+              (cond (proc
+                     (##sys#check-closure proc loc)
+                     (##sys#setslot (##sys#slot crt slot) i (wrap proc)))
+                    (else
+                     (##sys#setslot (##sys#slot crt slot) i #f))))))))
  
   (set! set-read-syntax!
     (syntax-setter
diff --git a/manual/Unit library b/manual/Unit library
index 2bc1045..232d42c 100644
--- a/manual/Unit library       
+++ b/manual/Unit library       
@@ -1224,6 +1224,8 @@ To disable built-in read-syntax, define a handler that 
triggers an error (for ex
 Similar to {{set-read-syntax!}}, but allows defining new {{#<CHAR> ...}} 
reader syntax.
 If the first argument is a symbol, then this procedure is equivalent to 
{{set-read-syntax!}}.
 
+{{PROC}} may be {{#f}} to disable previously defined "sharp" read syntax.
+
 
 ==== set-parameterized-read-syntax!
 
@@ -1235,6 +1237,8 @@ arguments: the input port and the number preceding
 the dispatching character.
 If the first argument is a symbol, then this procedure is equivalent to 
{{set-read-syntax!}}.
 
+{{PROC}} may be {{#f}} to disable previously defined parameterized read syntax.
+
 
 ==== copy-read-table
 
diff --git a/types.db b/types.db
index 940c6e0..c116f7c 100644
--- a/types.db
+++ b/types.db
@@ -1034,13 +1034,18 @@
 (set-gc-report! (#(procedure #:clean) set-gc-report! (*) undefined))
 
 (set-parameterized-read-syntax!
- (#(procedure #:clean #:enforce) set-parameterized-read-syntax! (char 
(procedure (input-port fixnum) . *)) undefined))
+ (#(procedure #:clean #:enforce) set-parameterized-read-syntax!
+  (char (or boolean (procedure (input-port fixnum) . *))) undefined))
 
 (set-port-name! (#(procedure #:clean #:enforce) set-port-name! (port string) 
undefined)
                ((port string) (##sys#setslot #(1) '3 #(2))))
 
-(set-read-syntax! (#(procedure #:clean #:enforce) set-read-syntax! (char 
(procedure (input-port) . *)) undefined))
-(set-sharp-read-syntax! (#(procedure #:clean #:enforce) set-sharp-read-syntax! 
(char (procedure (input-port) . *)) undefined))
+(set-read-syntax! (#(procedure #:clean #:enforce) set-read-syntax!
+                  (char (or boolean (procedure (input-port) . *))) undefined))
+
+(set-sharp-read-syntax! (#(procedure #:clean #:enforce) set-sharp-read-syntax!
+                        (char (or boolean (procedure (input-port) . *))) 
undefined))
+
 (setter (#(procedure #:clean #:enforce) setter (procedure) procedure))
 (signal (procedure signal (*) . *))
 (signum (#(procedure #:clean #:enforce) signum (number) number))
-- 
1.7.0.4