One more step towards working Mac SCons build....

webkit/build/port/SConscript

 # Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os.path
 import re
 
 Import('env')
 
 webcore = env.Dir('$CHROME_SRC_DIR/third_party/WebKit/WebCore')
@@ skipping 554 matching lines @@
   t = str(target[1])
   fp = open(t, 'w')
   define = os.path.splitext(os.path.split(t)[1])[0]
   fp.write('#ifndef %s_h\n' % define)
   fp.write('#define %s_h\n' % define)
   fp.write(open(t + 'pp', 'r').read())
   fp.write('#endif // %s_h\n' % define)
 
 # TODO(sgk):  make this a real pseudo-Builder
 def BuildYacc(env, dir, name, file):
-  env.Command(['$DERIVED_DIR/%s.cpp' % file,
-               '$DERIVED_DIR/%s.h'   % file],
-              ['$PORT_DIR/%s/%s.y' % (dir, file)],
-              ['$YACC -d -p %s ${SOURCES[0].posix} ' % name +
-                 '-o ${TARGET.posix}',
-               Action(create_h_wrapper),
-               Delete('${TARGETS[1]}pp')])
+  yacc_env = env.Clone()
+  yacc_env['YACC'] = env.Detect('bison') or 'yacc'
+  yacc_env.Command(['$DERIVED_DIR/%s.cpp' % file,
+                    '$DERIVED_DIR/%s.h'   % file],
+                   ['$PORT_DIR/%s/%s.y' % (dir, file)],
+                   ['$YACC -d -p %s ${SOURCES[0].posix} ' % name +
+                      '-o ${TARGET.posix}',
+                    Action(create_h_wrapper),
+                    Delete('${TARGETS[1]}pp')])
 
 BuildYacc(env, 'xml', 'xpathyy', 'XPathGrammar')
 BuildYacc(env, 'css', 'cssyy',   'CSSGrammar')
 
 # TODO(bradnelson): need to add in error checking
 
 env.Command('$PORT_DIR/SVGCSSValueKeywords.in',
             '$PORT_DIR/css/SVGCSSValueKeywords.in',
             '$PERL -ne "print lc" $SOURCES > $TARGET')
 
@@ skipping 43 matching lines @@
 env.Command('$DERIVED_DIR/HTMLEntityNames.c',
             '$PORT_DIR/html/HTMLEntityNames.gperf',
             'gperf -a -L ANSI-C -C -G -c -o -t -k "*" -N findEntity ' + \
             '-D -s 2 $SOURCE > $TARGET')
 
 # CSS tokenizer
 env.Command('$DERIVED_DIR/tokenizer.cpp',
             ['$PORT_DIR/css/tokenizer.flex',
              '$PORT_DIR/css/maketokenizer'],
             'flex --nowarn -t $SOURCE | perl ${SOURCES[1]} > $TARGET')