Added an exception handler and error msg.
header {* String examples *}
theory StringEx = Main:
lemma "hd ''ABCD'' = CHR ''A''"
by simp
lemma "hd ''ABCD'' \<noteq> CHR ''B''"
by simp
lemma "''ABCD'' \<noteq> ''ABCX''"
by simp
lemma "''ABCD'' = ''ABCD''"
by simp
lemma "''ABCDEFGHIJKLMNOPQRSTUVWXYZ'' \<noteq>
''ABCDEFGHIJKLMNOPQRSTUVWXY''"
by simp
lemma "set ''Foobar'' = {CHR ''F'', CHR ''a'', CHR ''b'', CHR ''o'', CHR ''r''}"
by (simp add: insert_commute)
lemma "set ''Foobar'' = ?X"
by (simp add: insert_commute)
end