aboutsummaryrefslogtreecommitdiffstats
path: root/lib/stdlib/doc/src/erl_eval.xml
diff options
context:
space:
mode:
authorErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
committerErlang/OTP <[email protected]>2009-11-20 14:54:40 +0000
commit84adefa331c4159d432d22840663c38f155cd4c1 (patch)
treebff9a9c66adda4df2106dfd0e5c053ab182a12bd /lib/stdlib/doc/src/erl_eval.xml
downloadotp-84adefa331c4159d432d22840663c38f155cd4c1.tar.gz
otp-84adefa331c4159d432d22840663c38f155cd4c1.tar.bz2
otp-84adefa331c4159d432d22840663c38f155cd4c1.zip
The R13B03 release.OTP_R13B03
Diffstat (limited to 'lib/stdlib/doc/src/erl_eval.xml')
-rw-r--r--lib/stdlib/doc/src/erl_eval.xml246
1 files changed, 246 insertions, 0 deletions
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 D&auml;cker</responsible>
+ <docno>1</docno>
+ <approved>Bjarne D&auml;cker</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>
+