Unsecure assoc calls (was: Make default margin values depend on paper size)

[Michael Käppler]

Hi Carl,
(was it your intention to discuss this off-list? I ask because you 
didn't cc the list for the last two times.)
> Hmmm -- I see your point.
>
> Without looking into the code for each of those grep results, I couldn't
> answer.  But assoc-get is defined in LilyPond, and was certainly recommended
> by Han-Wen when I first started programming Scheme in LilyPOnd.
>
> I wonder if I'm being overly sensitive, or if many of these assoc calls are
> left over from before assoc-get was defined.
I would propose to modify assoc-get the way it is indicated in the 
attached patch and then migrate all assoc calls to assoc-get calls.
This assoc-get calls would be divided into two classes.
1. Silently set a default value, since there is nothing erroneous happening.
2. Set a default value and output a programming_error, showing the key 
which failed.

Of course that would also happen with chain-assoc-get.
I also recognized that some assoc-get or chain-assoc-get calls occur 
with #f set as default value, which I think is unnecessary since #f is 
the hardcoded default already.

Regards,
Michael

>From 5fb65494ecb7e25d87fdfea6ce2133a818631df8 Mon Sep 17 00:00:00 2001
From: =?utf-8?q?Michael=20K=C3=A4ppler?= <address@hidden>
Date: Fri, 11 Sep 2009 11:44:32 +0200
Subject: [PATCH] Proposal to change ly:assoc-get method.

---
 lily/general-scheme.cc |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/lily/general-scheme.cc b/lily/general-scheme.cc
index 43ff745..d6dffb9 100644
--- a/lily/general-scheme.cc
+++ b/lily/general-scheme.cc
@@ -155,7 +155,7 @@ LY_DEFINE (ly_dir_p, "ly:dir?",
 
 LY_DEFINE (ly_assoc_get, "ly:assoc-get",
           2, 1, 0,
-          (SCM key, SCM alist, SCM default_value),
+          (SCM key, SCM alist, SCM default_value, SCM strict_checking),
           "Return value if @var{key} in @var{alist}, else @code{default-value}"
           " (or @code{#f} if not specified).")
 {
@@ -168,6 +168,9 @@ LY_DEFINE (ly_assoc_get, "ly:assoc-get",
   if (default_value == SCM_UNDEFINED)
     default_value = SCM_BOOL_F;
 
+  if (strict_checking == SCM_BOOL_T)
+    programming_error ("Cannot find key ~S in alist, setting to ~S.", 
ly_scm2string (key), ly_scm2string (default_value));
+
   return default_value;
 }
 
-- 
1.6.0.2