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| -rw-r--r-- | erts/doc/src/match_spec.xml | 74 |
1 files changed, 54 insertions, 20 deletions
diff --git a/erts/doc/src/match_spec.xml b/erts/doc/src/match_spec.xml index ca73d78b8d..7be3d15de6 100644 --- a/erts/doc/src/match_spec.xml +++ b/erts/doc/src/match_spec.xml @@ -33,21 +33,15 @@ <file>match_spec.xml</file> </header> <p>A "match specification" (match_spec) is an Erlang term describing a - small "program" that will try to match something (either the - parameters to a function as used in the <c><![CDATA[erlang:trace_pattern/2]]></c> - BIF, or the objects in an ETS table.). + small "program" that will try to match something. It can be used + to either control tracing with + <seealso marker="erlang#trace_pattern/3">erlang:trace_pattern/3</seealso> + or to search for objects in an ETS table with for example + <seealso marker="stdlib:ets#select/2">ets:select/2</seealso>. The match_spec in many ways works like a small function in Erlang, but is interpreted/compiled by the Erlang runtime system to something much more efficient than calling an Erlang function. The match_spec is also very limited compared to the expressiveness of real Erlang functions.</p> - <p>Match specifications are given to the BIF <c><![CDATA[erlang:trace_pattern/2]]></c> to - execute matching of function arguments as well as to define some actions - to be taken when the match succeeds (the <c><![CDATA[MatchBody]]></c> part). Match - specifications can also be used in ETS, to specify objects to be - returned from an <c><![CDATA[ets:select/2]]></c> call (or other select - calls). The semantics and restrictions differ slightly when using - match specifications for tracing and in ETS, the differences are - defined in a separate paragraph below.</p> <p>The most notable difference between a match_spec and an Erlang fun is of course the syntax. Match specifications are Erlang terms, not Erlang code. A match_spec also has a somewhat strange concept of @@ -382,6 +376,51 @@ the pid() of the current process.</p> </section> + <marker id="match_target"></marker> + <section> + <title>Match target</title> + <p>Each execution of a match specification is done against + a match target term. The format and content of the target term + depends on the context in which the match is done. The match + target for ETS is always a full table tuple. The match target + for call trace is always a list of all function arguments. The + match target for event trace depends on the event type, see + table below.</p> + <table> + <row> + <cell align="left" valign="middle">Context</cell> + <cell align="left" valign="middle">Type</cell> + <cell align="left" valign="middle">Match target</cell> + <cell align="left" valign="middle">Description</cell> + </row> + <row> + <cell align="left" valign="middle">ETS</cell> + <cell align="left" valign="middle"></cell> + <cell align="left" valign="middle">{Key, Value1, Value2, ...}</cell> + <cell align="left" valign="middle">A table object</cell> + </row> + <row> + <cell align="left" valign="middle">Trace</cell> + <cell align="left" valign="middle">call</cell> + <cell align="left" valign="middle">[Arg1, Arg2, ...]</cell> + <cell align="left" valign="middle">Function arguments</cell> + </row> + <row> + <cell align="left" valign="middle">Trace</cell> + <cell align="left" valign="middle">send</cell> + <cell align="left" valign="middle">[Receiver, Message]</cell> + <cell align="left" valign="middle">Receiving process/port and message term</cell> + </row> + <row> + <cell align="left" valign="middle">Trace</cell> + <cell align="left" valign="middle">'receive'</cell> + <cell align="left" valign="middle">[Node, Sender, Message]</cell> + <cell align="left" valign="middle">Sending node, process/port and message term</cell> + </row> + <tcaption>Match target depending on context</tcaption> + </table> + </section> + <section> <title>Variables and literals</title> <p>Variables take the form <c><![CDATA['$<number>']]></c> where @@ -396,10 +435,8 @@ <c><![CDATA[MatchCondition]]></c> parts, only variables bound previously may be used. As a special case, in the <c><![CDATA[MatchCondition/MatchBody]]></c> parts, the variable <c><![CDATA['$_']]></c> - expands to the whole expression which matched the - <c><![CDATA[MatchHead]]></c> (i.e., the whole parameter list to the possibly - traced function or the whole matching object in the ets table) - and the variable <c><![CDATA['$$']]></c> expands to a list + expands to the whole <seealso marker="#match_target">match target</seealso> + term and the variable <c><![CDATA['$$']]></c> expands to a list of the values of all bound variables in order (i.e. <c><![CDATA[['$1','$2', ...]]]></c>). </p> @@ -480,8 +517,8 @@ <p>For each tuple in the <c><![CDATA[MatchExpression]]></c> list and while no match has succeeded:</p> <list type="bulleted"> - <item>Match the <c><![CDATA[MatchHead]]></c> part against the arguments to the - function, + <item>Match the <c><![CDATA[MatchHead]]></c> part against the + match target term, binding the <c><![CDATA['$<number>']]></c> variables (much like in <c><![CDATA[ets:match/2]]></c>). If the <c><![CDATA[MatchHead]]></c> cannot match the arguments, the match fails. @@ -522,9 +559,6 @@ term. The <c><![CDATA[ActionTerm]]></c>'s are executed as in an imperative language, i.e. for their side effects. Functions with side effects are also allowed when tracing.</p> - <p>In ETS the match head is a <c><![CDATA[tuple()]]></c> (or a single match - variable) while it is a list (or a single match variable) when - tracing.</p> </section> <section> |