--- a/doc-src/IsarImplementation/Thy/ML.thy Wed Oct 20 20:47:06 2010 +0100
+++ b/doc-src/IsarImplementation/Thy/ML.thy Wed Oct 20 21:22:56 2010 +0100
@@ -726,6 +726,48 @@
*}
+subsection {* Association lists *}
+
+text {* The operations for association lists interpret a concrete list
+ of pairs as a finite function from keys to values. Redundant
+ representations with multiple occurrences of the same key are
+ implicitly normalized: lookup and update only take the first
+ occurrence into account.
+*}
+
+text {*
+ \begin{mldecls}
+ @{index_ML AList.lookup: "('a * 'b -> bool) -> ('b * 'c) list -> 'a -> 'c option"} \\
+ @{index_ML AList.defined: "('a * 'b -> bool) -> ('b * 'c) list -> 'a -> bool"} \\
+ @{index_ML AList.update: "('a * 'a -> bool) -> 'a * 'b -> ('a * 'b) list -> ('a * 'b) list"} \\
+ \end{mldecls}
+
+ \begin{description}
+
+ \item @{ML AList.lookup}, @{ML AList.defined}, @{ML AList.update}
+ implement the main ``framework operations'' for mappings in
+ Isabelle/ML, with standard conventions for names and types.
+
+ Note that a function called @{text lookup} is obliged to express its
+ partiality via an explicit option element. There is no choice to
+ raise an exception, without changing the name to something like
+ @{text "the_element"} or @{text "get"}.
+
+ The @{text "defined"} operation is essentially a contraction of @{ML
+ is_some} and @{text "lookup"}, but this is sufficiently frequent to
+ justify its independent existence. This also gives the
+ implementation some opportunity for peep-hole optimization.
+
+ \end{description}
+
+ Association lists are adequate as simple and light-weight
+ implementation of finite mappings in many practical situations. A
+ more heavy-duty table structure is defined in @{"file"
+ "~~/src/Pure/General/table.ML"}; that version scales easily to
+ thousands or millions of elements.
+*}
+
+
subsection {* Unsynchronized references *}
text %mlref {*