user=> (doc read-string)
-------------------------
clojure.core/read-string
([s])
Reads *one* object from the string s
nil
(emphasis on *one* by me)
one object from ":a(" = :a; ":a)" = :a; "( … " = fail; ")…" = fail. (remember
whitespace in front of a paren doesn't matter)
Have fun.
From: noahlz <[email protected]<mailto:[email protected]>>
Reply-To: Clojure <[email protected]<mailto:[email protected]>>
Date: Monday, April 29, 2013 16:26
To: Clojure <[email protected]<mailto:[email protected]>>
Subject: Understanding unmatched parenthesis in read-string
(Disclaimer: I post this aware that read-string is considered dangerous for
untrusted code and having starred tools.reader)
I was writing some code using read-string and encountered the following
(somewhat odd?) behavior:
Clojure 1.5.1
user=> (read-string "1000N(")
1000N
user=> (read-string "1000N)")
1000N
user=> (read-string "(1000N")
RuntimeException EOF while reading clojure.lang.Util.runtimeException
(Util.java:219)
user=> (read-string ")1000N")
RuntimeException Unmatched delimiter: ) clojure.lang.Util.runtimeException
(Util.java:219)
So if the string ends with an unmatched ) or (, the preceding value gets
returned and the unmatched character discarded. But if the string starts with
an unmatched parens - EOF (as expected). I was a little surprised as I expected
the first to cases to throw some kind of RuntimeException.
What is the explanation for this behavior if any, and where can I go / read
more about the underlying theory of "correctly" handling this case? I'm aware
that lexical parsing is a big topic - just wondering what the ruling was here
(if any) and looking for a jumping off point into further readings. Also if
this was discussed elsewhere (searching "read-string unmatched paren" yielded
nothing).
Thanks!
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