<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
<copyright>
<year>1996</year><year>2010</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
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Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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</legalnotice>
<title>erl_parse</title>
<prepared>Robert</prepared>
<responsible>Bjarne Däcker</responsible>
<docno>1</docno>
<approved>Bjarne Däcker</approved>
<checked></checked>
<date>97-01-24</date>
<rev>B</rev>
<file>erl_parse.sgml</file>
</header>
<module>erl_parse</module>
<modulesummary>The Erlang Parser</modulesummary>
<description>
<p>This module is the basic Erlang parser which converts tokens into
the abstract form of either forms (i.e., top-level constructs),
expressions, or terms. The Abstract Format is described in the ERTS
User's Guide.
Note that a token list must end with the <em>dot</em> token in order
to be acceptable to the parse functions (see erl_scan).</p>
</description>
<funcs>
<func>
<name>parse_form(Tokens) -> {ok, AbsForm} | {error, ErrorInfo}</name>
<fsummary>Parse an Erlang form</fsummary>
<type>
<v>Tokens = [Token]</v>
<v>Token = {Tag,Line} | {Tag,Line,term()}</v>
<v>Tag = atom()</v>
<v>AbsForm = term()</v>
<v>ErrorInfo = see section Error Information below.</v>
</type>
<desc>
<p>This function parses <c>Tokens</c> as if it were a form. It returns:</p>
<taglist>
<tag><c>{ok, AbsForm}</c></tag>
<item>
<p>The parsing was successful. <c>AbsForm</c> is the
abstract form of the parsed form.</p>
</item>
<tag><c>{error, ErrorInfo}</c></tag>
<item>
<p>An error occurred.</p>
</item>
</taglist>
</desc>
</func>
<func>
<name>parse_exprs(Tokens) -> {ok, Expr_list} | {error, ErrorInfo}</name>
<fsummary>Parse Erlang expressions</fsummary>
<type>
<v>Tokens = [Token]</v>
<v>Token = {Tag,Line} | {Tag,Line,term()}</v>
<v>Tag = atom()</v>
<v>Expr_list = [AbsExpr]</v>
<v>AbsExpr = term()</v>
<v>ErrorInfo = see section Error Information below.</v>
</type>
<desc>
<p>This function parses <c>Tokens</c> as if it were a list of expressions. It returns:</p>
<taglist>
<tag><c>{ok, Expr_list}</c></tag>
<item>
<p>The parsing was successful. <c>Expr_list</c> is a
list of the abstract forms of the parsed expressions.</p>
</item>
<tag><c>{error, ErrorInfo}</c></tag>
<item>
<p>An error occurred.</p>
</item>
</taglist>
</desc>
</func>
<func>
<name>parse_term(Tokens) -> {ok, Term} | {error, ErrorInfo}</name>
<fsummary>Parse an Erlang term</fsummary>
<type>
<v>Tokens = [Token]</v>
<v>Token = {Tag,Line} | {Tag,Line,term()}</v>
<v>Tag = atom()</v>
<v>Term = term()</v>
<v>ErrorInfo = see section Error Information below.</v>
</type>
<desc>
<p>This function parses <c>Tokens</c> as if it were a term. It returns:</p>
<taglist>
<tag><c>{ok, Term}</c></tag>
<item>
<p>The parsing was successful. <c>Term</c> is
the Erlang term corresponding to the token list.</p>
</item>
<tag><c>{error, ErrorInfo}</c></tag>
<item>
<p>An error occurred.</p>
</item>
</taglist>
</desc>
</func>
<func>
<name>format_error(ErrorDescriptor) -> Chars</name>
<fsummary>Format an error descriptor</fsummary>
<type>
<v>ErrorDescriptor = errordesc()</v>
<v>Chars = [char() | Chars]</v>
</type>
<desc>
<p>Uses an <c>ErrorDescriptor</c> and returns a string
which describes the error. This function is usually called
implicitly when an <c>ErrorInfo</c> structure is processed
(see below).</p>
</desc>
</func>
<func>
<name>tokens(AbsTerm) -> Tokens</name>
<name>tokens(AbsTerm, MoreTokens) -> Tokens</name>
<fsummary>Generate a list of tokens for an expression</fsummary>
<type>
<v>Tokens = MoreTokens = [Token]</v>
<v>Token = {Tag,Line} | {Tag,Line,term()}</v>
<v>Tag = atom()</v>
<v>AbsTerm = term()</v>
<v>ErrorInfo = see section Error Information below.</v>
</type>
<desc>
<p>This function generates a list of tokens representing the abstract
form <c>AbsTerm</c> of an expression. Optionally, it appends
<c>Moretokens</c>.</p>
</desc>
</func>
<func>
<name>normalise(AbsTerm) -> Data</name>
<fsummary>Convert abstract form to an Erlang term</fsummary>
<type>
<v>AbsTerm = Data = term()</v>
</type>
<desc>
<p>Converts the abstract form <c>AbsTerm</c> of a term into a
conventional Erlang data structure (i.e., the term itself).
This is the inverse of <c>abstract/1</c>.</p>
</desc>
</func>
<func>
<name>abstract(Data) -> AbsTerm</name>
<fsummary>Convert an Erlang term into an abstract form</fsummary>
<type>
<v>Data = AbsTerm = term()</v>
</type>
<desc>
<p>Converts the Erlang data structure <c>Data</c> into an
abstract form of type <c>AbsTerm</c>. This is the inverse of
<c>normalise/1</c>.</p>
</desc>
</func>
</funcs>
<section>
<title>Error Information</title>
<p>The <c>ErrorInfo</c> mentioned above is the standard
<c>ErrorInfo</c> structure which is returned from all IO
modules. It has the format:
</p>
<code type="none">
{ErrorLine, Module, ErrorDescriptor} </code>
<p>A string which describes the error is obtained with the following call:
</p>
<code type="none">
Module:format_error(ErrorDescriptor) </code>
</section>
<section>
<title>See Also</title>
<p><seealso marker="io">io(3)</seealso>,
<seealso marker="erl_scan">erl_scan(3)</seealso>,
ERTS User's Guide</p>
</section>
</erlref>
