====== Function MAPHASH ====== ====Syntax==== * **maphash** //function hash-table// → //**[[CL:Constant Variables:nil]]**// ====Arguments and Values==== * //function// - a //[[CL:Glossary:designator]]// for a //[[CL:Glossary:function]]// of two //[[CL:Glossary:arguments]]//, the //[[CL:Glossary:key]]// and the //[[CL:Glossary:value]]//. * //hash-table// - a //[[CL:Glossary:hash table]]//. ====Description==== Iterates over all entries in the //hash-table//. For each entry, the //function// is called with two //[[CL:Glossary:arguments]]//--the //[[CL:Glossary:key]]// and the //[[CL:Glossary:value]]// of that entry. The consequences are unspecified if any attempt is made to add or remove an entry from the //hash-table// while a **[[CL:Functions:maphash]]** is in progress, with two exceptions: the //function// can use can use **[[CL:Macros:setf]]** of **[[CL:Functions:gethash]]** to change the //[[CL:Glossary:value]]// part of the entry currently being processed, or it can use **[[CL:Functions:remhash]]** to remove that entry. ====Examples==== <blockquote> ([[CL:Macros:defparameter]] *table* ([[CL:Functions:make-hash-table]])) <r>*TABLE*</r> ([[CL:Macros:dotimes]] (i 10) ([[CL:Macros:setf]] ([[CL:Functions:gethash]] i *table*) i)) <r>[[CL:Constant Variables:nil|NIL]] </r> ([[CL:Special Operators:let]] ((sum-of-squares 0)) (maphash #'([[CL:Symbols:lambda]] (key val) ([[CL:Special Operators:let]] ((square ([[CL:Functions:math-multiply|*]] val val))) ([[CL:Macros:incf]] sum-of-squares square) ([[CL:Macros:setf]] ([[CL:Functions:gethash]] key *table*) square))) *table*) sum-of-squares) <r>285 </r> ([[CL:Functions:hash-table-count]] *table*) <r>10 </r> (maphash #'([[CL:Symbols:lambda]] (key val) ([[CL:Macros:when]] ([[CL:Functions:oddp]] val) ([[CL:Functions:remhash]] key *table*))) *table*) <r>[[CL:Constant Variables:nil|NIL]] </r> ([[CL:Functions:hash-table-count]] *table*) <r>5 </r> (maphash #'([[CL:Symbols:lambda]] (k v) ([[CL:Functions:print]] ([[CL:Functions:list]] k v))) *table*) <o>(0 0) (8 64) (2 4) (6 36) (4 16) </o> <r>[[CL:Constant Variables:nil|NIL]] </blockquote></r> ====Side Effects==== None, other than any which might be done by the //function//. ====Affected By==== None. ====Exceptional Situations==== None. ====See Also==== * **[[CL:Macros:loop|Macro LOOP]]** * **[[CL:Macros:with-hash-table-iterator|Macro WITH-HASH-TABLE-ITERATOR]]**, {\secref\TraversalRules} ====Notes==== None. \issue{MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE}