{"id":2955,"date":"2014-09-05T06:46:20","date_gmt":"2014-09-05T10:46:20","guid":{"rendered":"http:\/\/irreal.org\/blog\/?p=2955"},"modified":"2014-09-05T06:46:22","modified_gmt":"2014-09-05T10:46:22","slug":"temporary-syntax-tables-revisited","status":"publish","type":"post","link":"https:\/\/irreal.org\/blog\/?p=2955","title":{"rendered":"Temporary Syntax Tables Revisited"},"content":{"rendered":"

The other day, I wrote about Xah Lee’s post on temporary syntax tables<\/a> and the with-syntax-table<\/code> macro. Subsequently, Lee discovered a nasty side effect that he wrote about on the G+ Emacs Community<\/a> site. The problem was that his code <\/p>\n

\n
(with-syntax-table<\/span> (standard-syntax-table)\n  (modify-syntax-entry ?\\« \"(»\"<\/span>)\n  (modify-syntax-entry ?\\» \")«\"<\/span>)\n  ;; <\/span>…<\/span>\n  )\n<\/pre>\n<\/p><\/div>\n
 modified the original standard syntax table for all buffers. <\/p>\n
 The problem is (standard-syntax-table)<\/code> doesn’t copy the standard syntax table; it just returns a pointer to the standard syntax table object. This is the same thing that happens if you assign a list to a variable: <\/p>\n
\n
(setq<\/span> x '(1 2 3))\n(setq<\/span> y x)\n(setf (car y) 5)\n(message \"x is %s\"<\/span> x)\n<\/pre>\n<\/p><\/div>\n
 returns <\/p>\n
\nx is (5 2 3)\n<\/pre>\n
 because x<\/code> and y<\/code> refer to the same object. <\/p>\n
 What we need to do is first make a copy of the standard syntax table. Happily, the copy-syntax-table<\/code> function does just that1<\/a><\/sup> so if we evaluate <\/p>\n
\n
(with-syntax-table<\/span> (copy-syntax-table)\n  (modify-syntax-entry ?‹ \"(›\"<\/span>)\n  (describe-syntax))\n<\/pre>\n<\/p><\/div>\n
 the \u2039 is described as an open bracket but if we open a new fundamental buffer and call describe-syntax<\/code> it is described as punctuation, as expected. <\/p>\n
 Lee solved this problem<\/a> by creating a new syntax table with make-syntax-table<\/code> and added his definitions to it. You might think that Lee’s solution is incorrect because the other syntax definitions will be missing from his new table but it is<\/i> correct because make-syntax-table<\/code> will create a table that inherits from the standard syntax table (or whatever table you specify). <\/p>\n
\n
Footnotes: <\/h2>\n
\n
1<\/a><\/sup> <\/p>\n
 copy-syntax-table<\/code> copies standard syntax table by default but you can specify a table explicitly if you want to start with some other table. <\/p>\n<\/div><\/div>\n<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"
The other day, I wrote about Xah Lee’s post on temporary syntax tables and the with-syntax-table macro. Subsequently, Lee discovered a nasty side effect that he wrote about on the G+ Emacs Community site. The problem was that his code … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[18],"class_list":["post-2955","post","type-post","status-publish","format-standard","hentry","category-programming","tag-emacs"],"_links":{"self":[{"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2955","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2955"}],"version-history":[{"count":1,"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2955\/revisions"}],"predecessor-version":[{"id":2956,"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2955\/revisions\/2956"}],"wp:attachment":[{"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2955"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2955"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/irreal.org\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2955"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}