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<A HREF="http://www.erlang.se"><IMG BORDER=0 ALT="[Erlang Systems]" SRC="min_head.gif"></A>
<H1>erl_parse</H1>
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<H3>MODULE</H3>
<UL>
erl_parse</UL>
<H3>MODULE SUMMARY</H3>
<UL>
The Erlang Parser</UL>
<H3>DESCRIPTION</H3>
<UL>
<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.
Note that a token list must end with the <STRONG>dot</STRONG> token in order
to be acceptable to the parse functions (see erl_scan).
</UL>
<H3>EXPORTS</H3>
<P><A NAME="parse_form%1"><STRONG><CODE>parse_form(Tokens) -&#62; {ok, AbsForm} | {error, ErrorInfo}</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Tokens = [Token]</CODE></STRONG><BR>
<STRONG><CODE>Token = {Tag,Line} | {Tag,Line,term()}</CODE></STRONG><BR>
<STRONG><CODE>Tag = atom()</CODE></STRONG><BR>
<STRONG><CODE>AbsForm = term()</CODE></STRONG><BR>
<STRONG><CODE>ErrorInfo = see section Error Information below.</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>This function parses <CODE>Tokens</CODE> as if it were a form. It returns:
<P><DL>
<DT><CODE>{ok, AbsForm}</CODE></DT>
<DD> The parsing was successful. See section <A HREF="#ABSFORM">Abstract Form</A> below for a
description of <CODE>AbsForm</CODE>.
<BR>
</DD>
<DT><CODE>{error, ErrorInfo}</CODE></DT>
<DD>An error occurred.<BR>
</DD>
</DL>
</UL>
<P><A NAME="parse_exprs%1"><STRONG><CODE>parse_exprs(Tokens) -&#62; {ok, Expr_list} | {error, ErrorInfo}</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Tokens = [Token]</CODE></STRONG><BR>
<STRONG><CODE>Token = {Tag,Line} | {Tag,Line,term()}</CODE></STRONG><BR>
<STRONG><CODE>Tag = atom()</CODE></STRONG><BR>
<STRONG><CODE>Expr_list = [AbsExpr]</CODE></STRONG><BR>
<STRONG><CODE>AbsExpr = term()</CODE></STRONG><BR>
<STRONG><CODE>ErrorInfo = see section Error Information below.</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>This function parses <CODE>Tokens</CODE> as if it were a list of expressions. It returns:
<P><DL>
<DT><CODE>{ok, Expr_list}</CODE></DT>
<DD> The parsing was successful. <CODE>Expr_list</CODE> is a list
of the form <CODE>AbsExpr</CODE>, which is described in the
section <A HREF="#ABSFORM">Abstract
Form</A> below.
<BR>
</DD>
<DT><CODE>{error, ErrorInfo}</CODE></DT>
<DD>An error occurred.<BR>
</DD>
</DL>
</UL>
<P><A NAME="parse_term%1"><STRONG><CODE>parse_term(Tokens) -&#62; {ok, Term} | {error, ErrorInfo}</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Tokens = [Token]</CODE></STRONG><BR>
<STRONG><CODE>Token = {Tag,Line} | {Tag,Line,term()}</CODE></STRONG><BR>
<STRONG><CODE>Tag = atom()</CODE></STRONG><BR>
<STRONG><CODE>Term = term()</CODE></STRONG><BR>
<STRONG><CODE>ErrorInfo = see section Error Information below.</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>This function parses <CODE>Tokens</CODE> as if it were a term. It returns:
<P><DL>
<DT><CODE>{ok, Term}</CODE></DT>
<DD> The parsing was successful. <CODE>Term</CODE> is
         the Erlang term corresponding to the token list.
<BR>
</DD>
<DT><CODE>{error, ErrorInfo}</CODE></DT>
<DD>An error occurred.<BR>

</DD>
</DL>
</UL>
<P><A NAME="format_error%1"><STRONG><CODE>format_error(ErrorDescriptor) -&#62; string()</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>ErrorDescriptor = errordesc()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Uses an <CODE>ErrorDescriptor</CODE> and returns a string
which describes the error. This function is usually called
implicitly when an <CODE>ErrorInfo</CODE> structure is processed
(see below).
</UL>
<P><A NAME="tokens%1"><STRONG><CODE>tokens(AbsTerm) -&#62; Tokens</CODE></STRONG></A><BR>
<A NAME="tokens%2"><STRONG><CODE>tokens(AbsTerm, MoreTokens) -&#62; Tokens</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Tokens = MoreTokens = [Token]</CODE></STRONG><BR>
<STRONG><CODE>Token = {Tag,Line} | {Tag,Line,term()}</CODE></STRONG><BR>
<STRONG><CODE>Tag = atom()</CODE></STRONG><BR>
<STRONG><CODE>AbsTerm = term()</CODE></STRONG><BR>
<STRONG><CODE>ErrorInfo = see section Error Information below.</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>This function generates a list of tokens representing the abstract
        form <CODE>AbsTerm</CODE> of an expression. Optionally, it appends
        <CODE>Moretokens</CODE>.
</UL>
<P><A NAME="normalise%1"><STRONG><CODE>normalise(AbsTerm) -&#62; Data</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>AbsTerm = Data = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Converts the abstract form <CODE>AbsTerm</CODE> of a term into a
conventional Erlang data structure (i.e., the term itself).
         This is the inverse of <CODE>abstract/1</CODE>.
</UL>
<P><A NAME="abstract%1"><STRONG><CODE>abstract(Data) -&#62; AbsTerm</CODE></STRONG></A><BR>
<P><UL>Types:
<UL>
<STRONG><CODE>Data = AbsTerm = term()</CODE></STRONG><BR>
</UL>
</UL>
<UL>
<P>Converts the Erlang data structure <CODE>Data</CODE> into an
abstract form of type <CODE>AbsTerm</CODE>. This is the inverse of
         <CODE>normalise/1</CODE>.
</UL>
<H3>Abstract Form</H3>
<UL>
<A NAME="ABSFORM"><!-- Empty --></A><P>To be supplied</UL>
<H3>Error Information</H3>
<UL>
<P>The <CODE>ErrorInfo</CODE> mentioned above is the standard
<CODE>ErrorInfo</CODE> structure which is returned from all IO
modules. It has the format:

<PRE>    {ErrorLine, Module, ErrorDescriptor}</PRE><P>A string which describes the error is obtained with the following call:

<PRE>apply(Module, format_error, ErrorDescriptor)</PRE></UL>
<H3>See Also</H3>
<UL>
<P><A HREF="io.html">io</A>,
<A HREF="erl_scan.html">erl_scan</A>
</UL>
<H3>AUTHORS</H3>
<UL>
Robert Virding - support@erlang.ericsson.se<BR>
</UL>
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