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