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diff --git a/lib/stdlib/doc/src/erl_eval.xml b/lib/stdlib/doc/src/erl_eval.xml new file mode 100644 index 0000000000..62af23c5eb --- /dev/null +++ b/lib/stdlib/doc/src/erl_eval.xml @@ -0,0 +1,246 @@ +<?xml version="1.0" encoding="latin1" ?> +<!DOCTYPE erlref SYSTEM "erlref.dtd"> + +<erlref> + <header> + <copyright> + <year>1996</year><year>2009</year> + <holder>Ericsson AB. All Rights Reserved.</holder> + </copyright> + <legalnotice> + The contents of this file are subject to the Erlang Public License, + Version 1.1, (the "License"); you may not use this file except in + compliance with the License. You should have received a copy of the + Erlang Public License along with this software. If not, it can be + retrieved online at http://www.erlang.org/. + + Software distributed under the License is distributed on an "AS IS" + basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See + the License for the specific language governing rights and limitations + under the License. + + </legalnotice> + + <title>erl_eval</title> + <prepared>Robert Virding</prepared> + <responsible>Bjarne Däcker</responsible> + <docno>1</docno> + <approved>Bjarne Däcker</approved> + <checked></checked> + <date>97-01-21</date> + <rev>B</rev> + <file>erl_eval.sgml</file> + </header> + <module>erl_eval</module> + <modulesummary>The Erlang Meta Interpreter</modulesummary> + <description> + <p>This module provides an interpreter for Erlang expressions. The + expressions are in the abstract syntax as returned by + <c>erl_parse</c>, the Erlang parser, or a call to + <c>io:parse_erl_exprs/2</c>.</p> + </description> + <funcs> + <func> + <name>exprs(Expressions, Bindings) -> {value, Value, NewBindings}</name> + <name>exprs(Expressions, Bindings, LocalFunctionHandler) -> {value, Value, NewBindings}</name> + <name>exprs(Expressions, Bindings, LocalFunctionHandler, NonlocalFunctionHandler) -> {value, Value, NewBindings}</name> + <fsummary>Evaluate expressions</fsummary> + <type> + <v>Expressions = as returned by erl_parse or io:parse_erl_exprs/2</v> + <v>Bindings = as returned by bindings/1</v> + <v>LocalFunctionHandler = {value, Func} | {eval, Func} | none</v> + <v>NonlocalFunctionHandler = {value, Func} | none</v> + </type> + <desc> + <p>Evaluates <c>Expressions</c> with the set of bindings + <c>Bindings</c>, where <c>Expressions</c> is a sequence of + expressions (in abstract syntax) of a type which may be + returned by <c>io:parse_erl_exprs/2</c>. See below for an + explanation of how and when to use the arguments + <c>LocalFunctionHandler</c> and <c>NonlocalFunctionHandler</c>. + </p> + <p>Returns <c>{value, Value, NewBindings}</c></p> + </desc> + </func> + <func> + <name>expr(Expression, Bindings) -> { value, Value, NewBindings }</name> + <name>expr(Expression, Bindings, LocalFunctionHandler) -> { value, Value, NewBindings }</name> + <name>expr(Expression, Bindings, LocalFunctionHandler, NonlocalFunctionHandler) -> { value, Value, NewBindings }</name> + <name>expr(Expression, Bindings, LocalFunctionHandler, NonlocalFunctionHandler, ReturnFormat) -> { value, Value, NewBindings } | Value</name> + <fsummary>Evaluate expression</fsummary> + <type> + <v>Expression = as returned by io:parse_erl_form/2, for example</v> + <v>Bindings = as returned by bindings/1</v> + <v>LocalFunctionHandler = {value, Func} | {eval, Func} | none</v> + <v>NonlocalFunctionHandler = {value, Func} | none</v> + <v>ReturnFormat = value | none</v> + </type> + <desc> + <p>Evaluates <c>Expression</c> with the set of bindings + <c>Bindings</c>. <c>Expression</c> is an expression (in + abstract syntax) of a type which may be returned by + <c>io:parse_erl_form/2</c>. See below for an explanation of + how and when to use the arguments + <c>LocalFunctionHandler</c> and + <c>NonlocalFunctionHandler</c>. + </p> + <p>Returns <c>{value, Value, NewBindings}</c> by default. But + if the <c>ReturnFormat</c> is <c>value</c> only the <c>Value</c> + is returned.</p> + </desc> + </func> + <func> + <name>expr_list(ExpressionList, Bindings) -> {ValueList, NewBindings}</name> + <name>expr_list(ExpressionList, Bindings, LocalFunctionHandler) -> {ValueList, NewBindings}</name> + <name>expr_list(ExpressionList, Bindings, LocalFunctionHandler, NonlocalFunctionHandler) -> {ValueList, NewBindings}</name> + <fsummary>Evaluate a list of expressions</fsummary> + <desc> + <p>Evaluates a list of expressions in parallel, using the same + initial bindings for each expression. Attempts are made to + merge the bindings returned from each evaluation. This + function is useful in the <c>LocalFunctionHandler</c>. See below. + </p> + <p>Returns <c>{ValueList, NewBindings}</c>.</p> + </desc> + </func> + <func> + <name>new_bindings() -> BindingStruct</name> + <fsummary>Return a bindings structure</fsummary> + <desc> + <p>Returns an empty binding structure.</p> + </desc> + </func> + <func> + <name>bindings(BindingStruct) -> Bindings</name> + <fsummary>Return bindings</fsummary> + <desc> + <p>Returns the list of bindings contained in the binding + structure.</p> + </desc> + </func> + <func> + <name>binding(Name, BindingStruct) -> Binding</name> + <fsummary>Return bindings</fsummary> + <desc> + <p>Returns the binding of <c>Name</c> in <c>BindingStruct</c>.</p> + </desc> + </func> + <func> + <name>add_binding(Name, Value, Bindings) -> BindingStruct</name> + <fsummary>Add a binding</fsummary> + <desc> + <p>Adds the binding <c>Name = Value</c> to <c>Bindings</c>. + Returns an updated binding structure.</p> + </desc> + </func> + <func> + <name>del_binding(Name, Bindings) -> BindingStruct</name> + <fsummary>Delete a binding</fsummary> + <desc> + <p>Removes the binding of <c>Name</c> in <c>Bindings</c>. + Returns an updated binding structure.</p> + </desc> + </func> + </funcs> + + <section> + <title>Local Function Handler</title> + <p>During evaluation of a function, no calls can be made to local + functions. An undefined function error would be + generated. However, the optional argument + <c>LocalFunctionHandler</c> may be used to define a function + which is called when there is a call to a local function. The + argument can have the following formats:</p> + <taglist> + <tag><c>{value,Func}</c></tag> + <item> + <p>This defines a local function handler which is called with:</p> + <code type="none"> +Func(Name, Arguments) </code> + <p><c>Name</c> is the name of the local function (an atom) and + <c>Arguments</c> is a list of the <em>evaluated</em> + arguments. The function handler returns the value of the + local function. In this case, it is not possible to access + the current bindings. To signal an error, the function + handler just calls <c>exit/1</c> with a suitable exit value.</p> + </item> + <tag><c>{eval,Func}</c></tag> + <item> + <p>This defines a local function handler which is called with:</p> + <code type="none"> +Func(Name, Arguments, Bindings) </code> + <p><c>Name</c> is the name of the local function (an atom), + <c>Arguments</c> is a list of the <em>unevaluated</em> + arguments, and <c>Bindings</c> are the current variable + bindings. The function handler returns:</p> + <code type="none"> +{value,Value,NewBindings} </code> + <p><c>Value</c> is the value of the local function and + <c>NewBindings</c> are the updated variable bindings. In + this case, the function handler must itself evaluate all the + function arguments and manage the bindings. To signal an + error, the function handler just calls <c>exit/1</c> with a + suitable exit value.</p> + </item> + <tag><c>none</c></tag> + <item> + <p>There is no local function handler.</p> + </item> + </taglist> + </section> + + <section> + <title>Non-local Function Handler</title> + <p>The optional argument <c>NonlocalFunctionHandler</c> may be + used to define a function which is called in the following + cases: a functional object (fun) is called; a built-in function + is called; a function is called using the M:F syntax, where M + and F are atoms or expressions; an operator Op/A is called + (this is handled as a call to the function <c>erlang:Op/A</c>). + Exceptions are calls to <c>erlang:apply/2,3</c>; neither of the + function handlers will be called for such calls. + The argument can have the following formats:</p> + <taglist> + <tag><c>{value,Func}</c></tag> + <item> + <p>This defines an nonlocal function handler which is called with:</p> + <code type="none"> +Func(FuncSpec, Arguments) </code> + <p><c>FuncSpec</c> is the name of the function on the form + <c>{Module,Function}</c> or a fun, and <c>Arguments</c> is a + list of the <em>evaluated</em> arguments. The function + handler returns the value of the function. To + signal an error, the function handler just calls + <c>exit/1</c> with a suitable exit value.</p> + </item> + <tag><c>none</c></tag> + <item> + <p>There is no nonlocal function handler.</p> + </item> + </taglist> + <note> + <p>For calls such as <c>erlang:apply(Fun, Args)</c> or + <c>erlang:apply(Module, Function, Args)</c> the call of the + non-local function handler corresponding to the call to + <c>erlang:apply/2,3</c> itself--<c>Func({erlang, apply}, [Fun, Args])</c> or <c>Func({erlang, apply}, [Module, Function, Args])</c>--will never take place. The non-local function + handler <em>will</em> however be called with the evaluated + arguments of the call to <c>erlang:apply/2,3</c>: <c>Func(Fun, Args)</c> or <c>Func({Module, Function}, Args)</c> (assuming + that <c>{Module, Function}</c> is not <c>{erlang, apply}</c>).</p> + <p>Calls to functions defined by evaluating fun expressions + <c>"fun ... end"</c> are also hidden from non-local function + handlers.</p> </note> + <p>The nonlocal function handler argument is probably not used as + frequently as the local function handler argument. A possible + use is to call <c>exit/1</c> on calls to functions that for some + reason are not allowed to be called.</p> + </section> + + <section> + <title>Bugs</title> + <p>The evaluator is not complete. <c>receive</c> cannot be + handled properly. + </p> + <p>Any undocumented functions in <c>erl_eval</c> should not be used.</p> + </section> +</erlref> + |