(* Author: Tobias Nipkow *)
theory Util imports Main
begin
subsection "Show sets of variables as lists"
text {* Sets are functions and are not displayed by element if
computed as values: *}
value "{''x'', ''y''}"
text {* Lists do not have this problem *}
value "[''x'', ''y'']"
text {* We define a function @{text show} that converts a set of
variable names into a list. To keep things simple, we rely on
the convention that we only use single letter names.
*}
definition
letters :: "string list" where
"letters = map (\<lambda>c. [c]) chars"
definition
"show" :: "string set \<Rightarrow> string list" where
"show S = filter S letters"
value "show {''x'', ''z''}"
end