<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
<header>
<copyright>
<year>2001</year><year>2013</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>The Abstract Format</title>
<prepared>Arndt Jonasson</prepared>
<responsible>Kenneth Lundin</responsible>
<docno>1</docno>
<approved>Jultomten</approved>
<checked></checked>
<date>00-12-01</date>
<rev>A</rev>
<file>absform.xml</file>
</header>
<p></p>
<p>This document describes the standard representation of parse trees for Erlang
programs as Erlang terms. This representation is known as the <em>abstract format</em>.
Functions dealing with such parse trees are <c><![CDATA[compile:forms/[1,2]]]></c>
and functions in the modules
<c><![CDATA[epp]]></c>,
<c><![CDATA[erl_eval]]></c>,
<c><![CDATA[erl_lint]]></c>,
<c><![CDATA[erl_pp]]></c>,
<c><![CDATA[erl_parse]]></c>,
and
<c><![CDATA[io]]></c>.
They are also used as input and output for parse transforms (see the module
<c><![CDATA[compile]]></c>).</p>
<p>We use the function <c><![CDATA[Rep]]></c> to denote the mapping from an Erlang source
construct <c><![CDATA[C]]></c> to its abstract format representation <c><![CDATA[R]]></c>, and write
<c><![CDATA[R = Rep(C)]]></c>.
</p>
<p>The word <c><![CDATA[LINE]]></c> below represents an integer, and denotes the
number of the line in the source file where the construction occurred.
Several instances of <c><![CDATA[LINE]]></c> in the same construction may denote
different lines.</p>
<p>Since operators are not terms in their own right, when operators are
mentioned below, the representation of an operator should be taken to
be the atom with a printname consisting of the same characters as the
operator.
</p>
<section>
<title>Module declarations and forms</title>
<p>A module declaration consists of a sequence of forms that are either
function declarations or attributes.</p>
<list type="bulleted">
<item>If D is a module declaration consisting of the forms
<c><![CDATA[F_1]]></c>, ..., <c><![CDATA[F_k]]></c>, then
Rep(D) = <c><![CDATA[[Rep(F_1), ..., Rep(F_k)]]]></c>.</item>
<item>If F is an attribute <c><![CDATA[-module(Mod)]]></c>, then
Rep(F) = <c><![CDATA[{attribute,LINE,module,Mod}]]></c>.</item>
<item>If F is an attribute <c><![CDATA[-export([Fun_1/A_1, ..., Fun_k/A_k])]]></c>, then
Rep(F) = <c><![CDATA[{attribute,LINE,export,[{Fun_1,A_1}, ..., {Fun_k,A_k}]}]]></c>.</item>
<item>If F is an attribute <c><![CDATA[-import(Mod,[Fun_1/A_1, ..., Fun_k/A_k])]]></c>, then
Rep(F) = <c><![CDATA[{attribute,LINE,import,{Mod,[{Fun_1,A_1}, ..., {Fun_k,A_k}]}}]]></c>.</item>
<item>If F is an attribute <c><![CDATA[-compile(Options)]]></c>, then
Rep(F) = <c><![CDATA[{attribute,LINE,compile,Options}]]></c>.</item>
<item>If F is an attribute <c><![CDATA[-file(File,Line)]]></c>, then
Rep(F) = <c><![CDATA[{attribute,LINE,file,{File,Line}}]]></c>.</item>
<item>If F is a record declaration <c><![CDATA[-record(Name,{V_1, ..., V_k})]]></c>, then
Rep(F) =
<c><![CDATA[{attribute,LINE,record,{Name,[Rep(V_1), ..., Rep(V_k)]}}]]></c>. For Rep(V), see below.</item>
<item>If F is a wild attribute <c><![CDATA[-A(T)]]></c>, then
Rep(F) = <c><![CDATA[{attribute,LINE,A,T}]]></c>.
<br></br></item>
<item>If F is a function declaration <c><![CDATA[Name Fc_1 ; ... ; Name Fc_k]]></c>,
where each <c><![CDATA[Fc_i]]></c> is a function clause with a
pattern sequence of the same length <c><![CDATA[Arity]]></c>, then
Rep(F) = <c><![CDATA[{function,LINE,Name,Arity,[Rep(Fc_1), ...,Rep(Fc_k)]}]]></c>.</item>
</list>
<section>
<title>Record fields</title>
<p>Each field in a record declaration may have an optional
explicit default initializer expression</p>
<list type="bulleted">
<item>If V is <c><![CDATA[A]]></c>, then
Rep(V) = <c><![CDATA[{record_field,LINE,Rep(A)}]]></c>.</item>
<item>If V is <c><![CDATA[A = E]]></c>, then
Rep(V) = <c><![CDATA[{record_field,LINE,Rep(A),Rep(E)}]]></c>.</item>
</list>
</section>
<section>
<title>Representation of parse errors and end of file</title>
<p>In addition to the representations of forms, the list that represents
a module declaration (as returned by functions in <c><![CDATA[erl_parse]]></c> and
<c><![CDATA[epp]]></c>) may contain tuples <c><![CDATA[{error,E}]]></c> and <c><![CDATA[{warning,W}]]></c>, denoting
syntactically incorrect forms and warnings, and <c><![CDATA[{eof,LINE}]]></c>, denoting an end
of stream encountered before a complete form had been parsed.</p>
</section>
</section>
<section>
<title>Atomic literals</title>
<p>There are five kinds of atomic literals, which are represented in the
same way in patterns, expressions and guards:</p>
<list type="bulleted">
<item>If L is an integer or character literal, then
Rep(L) = <c><![CDATA[{integer,LINE,L}]]></c>.</item>
<item>If L is a float literal, then
Rep(L) = <c><![CDATA[{float,LINE,L}]]></c>.</item>
<item>If L is a string literal consisting of the characters
<c><![CDATA[C_1]]></c>, ..., <c><![CDATA[C_k]]></c>, then
Rep(L) = <c><![CDATA[{string,LINE,[C_1, ..., C_k]}]]></c>.</item>
<item>If L is an atom literal, then
Rep(L) = <c><![CDATA[{atom,LINE,L}]]></c>.</item>
</list>
<p>Note that negative integer and float literals do not occur as such; they are
parsed as an application of the unary negation operator.</p>
</section>
<section>
<title>Patterns</title>
<p>If <c><![CDATA[Ps]]></c> is a sequence of patterns <c><![CDATA[P_1, ..., P_k]]></c>, then
Rep(Ps) = <c><![CDATA[[Rep(P_1), ..., Rep(P_k)]]]></c>. Such sequences occur as the
list of arguments to a function or fun.</p>
<p>Individual patterns are represented as follows:</p>
<list type="bulleted">
<item>If P is an atomic literal L, then Rep(P) = Rep(L).</item>
<item>If P is a compound pattern <c><![CDATA[P_1 = P_2]]></c>, then
Rep(P) = <c><![CDATA[{match,LINE,Rep(P_1),Rep(P_2)}]]></c>.</item>
<item>If P is a variable pattern <c><![CDATA[V]]></c>, then
Rep(P) = <c><![CDATA[{var,LINE,A}]]></c>,
where A is an atom with a printname consisting of the same characters as
<c><![CDATA[V]]></c>.</item>
<item>If P is a universal pattern <c><![CDATA[_]]></c>, then
Rep(P) = <c><![CDATA[{var,LINE,'_'}]]></c>.</item>
<item>If P is a tuple pattern <c><![CDATA[{P_1, ..., P_k}]]></c>, then
Rep(P) = <c><![CDATA[{tuple,LINE,[Rep(P_1), ..., Rep(P_k)]}]]></c>.</item>
<item>If P is a nil pattern <c><![CDATA[[]]]></c>, then
Rep(P) = <c><![CDATA[{nil,LINE}]]></c>.</item>
<item>If P is a cons pattern <c><![CDATA[[P_h | P_t]]]></c>, then
Rep(P) = <c><![CDATA[{cons,LINE,Rep(P_h),Rep(P_t)}]]></c>.</item>
<item>If E is a binary pattern <c><![CDATA[<<P_1:Size_1/TSL_1, ..., P_k:Size_k/TSL_k>>]]></c>, then
Rep(E) = <c><![CDATA[{bin,LINE,[{bin_element,LINE,Rep(P_1),Rep(Size_1),Rep(TSL_1)}, ..., {bin_element,LINE,Rep(P_k),Rep(Size_k),Rep(TSL_k)}]}]]></c>.
For Rep(TSL), see below.
An omitted <c><![CDATA[Size]]></c> is represented by <c><![CDATA[default]]></c>. An omitted <c><![CDATA[TSL]]></c>
(type specifier list) is represented by <c><![CDATA[default]]></c>.</item>
<item>If P is <c><![CDATA[P_1 Op P_2]]></c>, where <c><![CDATA[Op]]></c> is a binary operator (this
is either an occurrence of <c><![CDATA[++]]></c> applied to a literal string or character
list, or an occurrence of an expression that can be evaluated to a number
at compile time),
then Rep(P) = <c><![CDATA[{op,LINE,Op,Rep(P_1),Rep(P_2)}]]></c>.</item>
<item>If P is <c><![CDATA[Op P_0]]></c>, where <c><![CDATA[Op]]></c> is a unary operator (this is an
occurrence of an expression that can be evaluated to a number at compile
time), then Rep(P) = <c><![CDATA[{op,LINE,Op,Rep(P_0)}]]></c>.</item>
<item>If P is a record pattern <c><![CDATA[#Name{Field_1=P_1, ..., Field_k=P_k}]]></c>,
then Rep(P) =
<c><![CDATA[{record,LINE,Name, [{record_field,LINE,Rep(Field_1),Rep(P_1)}, ..., {record_field,LINE,Rep(Field_k),Rep(P_k)}]}]]></c>.</item>
<item>If P is <c><![CDATA[#Name.Field]]></c>, then
Rep(P) = <c><![CDATA[{record_index,LINE,Name,Rep(Field)}]]></c>.</item>
<item>If P is <c><![CDATA[( P_0 )]]></c>, then
Rep(P) = <c><![CDATA[Rep(P_0)]]></c>,
i.e., patterns cannot be distinguished from their bodies.</item>
</list>
<p>Note that every pattern has the same source form as some expression, and is
represented the same way as the corresponding expression.</p>
</section>
<section>
<title>Expressions</title>
<p>A body B is a sequence of expressions <c><![CDATA[E_1, ..., E_k]]></c>, and
Rep(B) = <c><![CDATA[[Rep(E_1), ..., Rep(E_k)]]]></c>.</p>
<p>An expression E is one of the following alternatives:</p>
<list type="bulleted">
<item>If P is an atomic literal <c><![CDATA[L]]></c>, then
Rep(P) = Rep(L).</item>
<item>If E is <c><![CDATA[P = E_0]]></c>, then
Rep(E) = <c><![CDATA[{match,LINE,Rep(P),Rep(E_0)}]]></c>.</item>
<item>If E is a variable <c><![CDATA[V]]></c>, then
Rep(E) = <c><![CDATA[{var,LINE,A}]]></c>,
where <c><![CDATA[A]]></c> is an atom with a printname consisting of the same
characters as <c><![CDATA[V]]></c>.</item>
<item>If E is a tuple skeleton <c><![CDATA[{E_1, ..., E_k}]]></c>, then
Rep(E) = <c><![CDATA[{tuple,LINE,[Rep(E_1), ..., Rep(E_k)]}]]></c>.</item>
<item>If E is <c><![CDATA[[]]]></c>, then
Rep(E) = <c><![CDATA[{nil,LINE}]]></c>.</item>
<item>If E is a cons skeleton <c><![CDATA[[E_h | E_t]]]></c>, then
Rep(E) = <c><![CDATA[{cons,LINE,Rep(E_h),Rep(E_t)}]]></c>.</item>
<item>If E is a binary constructor <c><![CDATA[<<V_1:Size_1/TSL_1, ..., V_k:Size_k/TSL_k>>]]></c>, then
Rep(E) = <c><![CDATA[{bin,LINE,[{bin_element,LINE,Rep(V_1),Rep(Size_1),Rep(TSL_1)}, ..., {bin_element,LINE,Rep(V_k),Rep(Size_k),Rep(TSL_k)}]}]]></c>.
For Rep(TSL), see below.
An omitted <c><![CDATA[Size]]></c> is represented by <c><![CDATA[default]]></c>. An omitted <c><![CDATA[TSL]]></c>
(type specifier list) is represented by <c><![CDATA[default]]></c>.</item>
<item>If E is <c><![CDATA[E_1 Op E_2]]></c>, where <c><![CDATA[Op]]></c> is a binary operator,
then Rep(E) = <c><![CDATA[{op,LINE,Op,Rep(E_1),Rep(E_2)}]]></c>.</item>
<item>If E is <c><![CDATA[Op E_0]]></c>, where <c><![CDATA[Op]]></c> is a unary operator, then
Rep(E) = <c><![CDATA[{op,LINE,Op,Rep(E_0)}]]></c>.</item>
<item>If E is <c><![CDATA[#Name{Field_1=E_1, ..., Field_k=E_k}]]></c>, then
Rep(E) =
<c><![CDATA[{record,LINE,Name, [{record_field,LINE,Rep(Field_1),Rep(E_1)}, ..., {record_field,LINE,Rep(Field_k),Rep(E_k)}]}]]></c>.</item>
<item>If E is <c><![CDATA[E_0#Name{Field_1=E_1, ..., Field_k=E_k}]]></c>, then
Rep(E) =
<c><![CDATA[{record,LINE,Rep(E_0),Name, [{record_field,LINE,Rep(Field_1),Rep(E_1)}, ..., {record_field,LINE,Rep(Field_k),Rep(E_k)}]}]]></c>.</item>
<item>If E is <c><![CDATA[#Name.Field]]></c>, then
Rep(E) = <c><![CDATA[{record_index,LINE,Name,Rep(Field)}]]></c>.</item>
<item>If E is <c><![CDATA[E_0#Name.Field]]></c>, then
Rep(E) = <c><![CDATA[{record_field,LINE,Rep(E_0),Name,Rep(Field)}]]></c>.</item>
<item>If E is <c><![CDATA[catch E_0]]></c>, then
Rep(E) = <c><![CDATA[{'catch',LINE,Rep(E_0)}]]></c>.</item>
<item>If E is <c><![CDATA[E_0(E_1, ..., E_k)]]></c>, then
Rep(E) = <c><![CDATA[{call,LINE,Rep(E_0),[Rep(E_1), ..., Rep(E_k)]}]]></c>.</item>
<item>If E is <c><![CDATA[E_m:E_0(E_1, ..., E_k)]]></c>, then
Rep(E) =
<c><![CDATA[{call,LINE,{remote,LINE,Rep(E_m),Rep(E_0)},[Rep(E_1), ..., Rep(E_k)]}]]></c>.</item>
<item>If E is a list comprehension <c><![CDATA[[E_0 || W_1, ..., W_k]]]></c>,
where each <c><![CDATA[W_i]]></c> is a generator or a filter, then
Rep(E) = <c><![CDATA[{lc,LINE,Rep(E_0),[Rep(W_1), ..., Rep(W_k)]}]]></c>. For Rep(W), see
below.</item>
<item>If E is a binary comprehension <c><![CDATA[<<E_0 || W_1, ..., W_k>>]]></c>,
where each <c><![CDATA[W_i]]></c> is a generator or a filter, then
Rep(E) = <c><![CDATA[{bc,LINE,Rep(E_0),[Rep(W_1), ..., Rep(W_k)]}]]></c>. For Rep(W), see
below.</item>
<item>If E is <c><![CDATA[begin B end]]></c>, where <c><![CDATA[B]]></c> is a body, then
Rep(E) = <c><![CDATA[{block,LINE,Rep(B)}]]></c>.</item>
<item>If E is <c><![CDATA[if Ic_1 ; ... ; Ic_k end]]></c>,
where each <c><![CDATA[Ic_i]]></c> is an if clause then
Rep(E) =
<c><![CDATA[{'if',LINE,[Rep(Ic_1), ..., Rep(Ic_k)]}]]></c>.</item>
<item>If E is <c><![CDATA[case E_0 of Cc_1 ; ... ; Cc_k end]]></c>,
where <c><![CDATA[E_0]]></c> is an expression and each <c><![CDATA[Cc_i]]></c> is a
case clause then
Rep(E) =
<c><![CDATA[{'case',LINE,Rep(E_0),[Rep(Cc_1), ..., Rep(Cc_k)]}]]></c>.</item>
<item>If E is <c><![CDATA[try B catch Tc_1 ; ... ; Tc_k end]]></c>,
where <c><![CDATA[B]]></c> is a body and each <c><![CDATA[Tc_i]]></c> is a catch clause then
Rep(E) =
<c><![CDATA[{'try',LINE,Rep(B),[],[Rep(Tc_1), ..., Rep(Tc_k)],[]}]]></c>.</item>
<item>If E is <c><![CDATA[try B of Cc_1 ; ... ; Cc_k catch Tc_1 ; ... ; Tc_n end]]></c>,
where <c><![CDATA[B]]></c> is a body,
each <c><![CDATA[Cc_i]]></c> is a case clause and
each <c><![CDATA[Tc_j]]></c> is a catch clause then
Rep(E) =
<c><![CDATA[{'try',LINE,Rep(B),[Rep(Cc_1), ..., Rep(Cc_k)],[Rep(Tc_1), ..., Rep(Tc_n)],[]}]]></c>.</item>
<item>If E is <c><![CDATA[try B after A end]]></c>,
where <c><![CDATA[B]]></c> and <c><![CDATA[A]]></c> are bodies then
Rep(E) =
<c><![CDATA[{'try',LINE,Rep(B),[],[],Rep(A)}]]></c>.</item>
<item>If E is <c><![CDATA[try B of Cc_1 ; ... ; Cc_k after A end]]></c>,
where <c><![CDATA[B]]></c> and <c><![CDATA[A]]></c> are a bodies and
each <c><![CDATA[Cc_i]]></c> is a case clause then
Rep(E) =
<c><![CDATA[{'try',LINE,Rep(B),[Rep(Cc_1), ..., Rep(Cc_k)],[],Rep(A)}]]></c>.</item>
<item>If E is <c><![CDATA[try B catch Tc_1 ; ... ; Tc_k after A end]]></c>,
where <c><![CDATA[B]]></c> and <c><![CDATA[A]]></c> are bodies and
each <c><![CDATA[Tc_i]]></c> is a catch clause then
Rep(E) =
<c><![CDATA[{'try',LINE,Rep(B),[],[Rep(Tc_1), ..., Rep(Tc_k)],Rep(A)}]]></c>.</item>
<item>If E is <c><![CDATA[try B of Cc_1 ; ... ; Cc_k catch Tc_1 ; ... ; Tc_n after A end]]></c>,
where <c><![CDATA[B]]></c> and <c><![CDATA[A]]></c> are a bodies,
each <c><![CDATA[Cc_i]]></c> is a case clause and
each <c><![CDATA[Tc_j]]></c> is a catch clause then
Rep(E) =
<c><![CDATA[{'try',LINE,Rep(B),[Rep(Cc_1), ..., Rep(Cc_k)],[Rep(Tc_1), ..., Rep(Tc_n)],Rep(A)}]]></c>.</item>
<item>If E is <c><![CDATA[receive Cc_1 ; ... ; Cc_k end]]></c>,
where each <c><![CDATA[Cc_i]]></c> is a case clause then
Rep(E) =
<c><![CDATA[{'receive',LINE,[Rep(Cc_1), ..., Rep(Cc_k)]}]]></c>.</item>
<item>If E is <c><![CDATA[receive Cc_1 ; ... ; Cc_k after E_0 -> B_t end]]></c>,
where each <c><![CDATA[Cc_i]]></c> is a case clause,
<c><![CDATA[E_0]]></c> is an expression and <c><![CDATA[B_t]]></c> is a body, then
Rep(E) =
<c><![CDATA[{'receive',LINE,[Rep(Cc_1), ..., Rep(Cc_k)],Rep(E_0),Rep(B_t)}]]></c>.</item>
<item>If E is <c><![CDATA[fun Name / Arity]]></c>, then
Rep(E) = <c><![CDATA[{'fun',LINE,{function,Name,Arity}}]]></c>.</item>
<item>If E is <c><![CDATA[fun Module:Name/Arity]]></c>, then
Rep(E) = <c><![CDATA[{'fun',LINE,{function,Rep(Module),Rep(Name),Rep(Arity)}}]]></c>.
(Before the R15 release: Rep(E) = <c><![CDATA[{'fun',LINE,{function,Module,Name,Arity}}]]></c>.)</item>
<item>If E is <c><![CDATA[fun Fc_1 ; ... ; Fc_k end]]></c>
where each <c><![CDATA[Fc_i]]></c> is a function clause then Rep(E) =
<c><![CDATA[{'fun',LINE,{clauses,[Rep(Fc_1), ..., Rep(Fc_k)]}}]]></c>.</item>
<item>If E is <c><![CDATA[( E_0 )]]></c>, then
Rep(E) = <c><![CDATA[Rep(E_0)]]></c>,
i.e., parenthesized expressions cannot be distinguished from their bodies.</item>
</list>
<section>
<title>Generators and filters</title>
<p>When W is a generator or a filter (in the body of a list or binary comprehension), then:</p>
<list type="bulleted">
<item>If W is a generator <c><![CDATA[P <- E]]></c>, where <c><![CDATA[P]]></c> is a pattern and <c><![CDATA[E]]></c>
is an expression, then
Rep(W) = <c><![CDATA[{generate,LINE,Rep(P),Rep(E)}]]></c>.</item>
<item>If W is a generator <c><![CDATA[P <= E]]></c>, where <c><![CDATA[P]]></c> is a pattern and <c><![CDATA[E]]></c>
is an expression, then
Rep(W) = <c><![CDATA[{b_generate,LINE,Rep(P),Rep(E)}]]></c>.</item>
<item>If W is a filter <c><![CDATA[E]]></c>, which is an expression, then
Rep(W) = <c><![CDATA[Rep(E)]]></c>.</item>
</list>
</section>
<section>
<title>Binary element type specifiers</title>
<p>A type specifier list TSL for a binary element is a sequence of type
specifiers <c><![CDATA[TS_1 - ... - TS_k]]></c>.
Rep(TSL) = <c><![CDATA[[Rep(TS_1), ..., Rep(TS_k)]]]></c>.</p>
<p>When TS is a type specifier for a binary element, then:</p>
<list type="bulleted">
<item>If TS is an atom <c><![CDATA[A]]></c>, Rep(TS) = <c><![CDATA[A]]></c>.</item>
<item>If TS is a couple <c><![CDATA[A:Value]]></c> where <c><![CDATA[A]]></c> is an atom and <c><![CDATA[Value]]></c>
is an integer, Rep(TS) = <c><![CDATA[{A, Value}]]></c>.</item>
</list>
</section>
</section>
<section>
<title>Clauses</title>
<p>There are function clauses, if clauses, case clauses
and catch clauses.</p>
<p>A clause <c><![CDATA[C]]></c> is one of the following alternatives:</p>
<list type="bulleted">
<item>If C is a function clause <c><![CDATA[( Ps ) -> B]]></c>
where <c><![CDATA[Ps]]></c> is a pattern sequence and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,Rep(Ps),[],Rep(B)}]]></c>.</item>
<item>If C is a function clause <c><![CDATA[( Ps ) when Gs -> B]]></c>
where <c><![CDATA[Ps]]></c> is a pattern sequence,
<c><![CDATA[Gs]]></c> is a guard sequence and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,Rep(Ps),Rep(Gs),Rep(B)}]]></c>.</item>
<item>If C is an if clause <c><![CDATA[Gs -> B]]></c>
where <c><![CDATA[Gs]]></c> is a guard sequence and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,[],Rep(Gs),Rep(B)}]]></c>.</item>
<item>If C is a case clause <c><![CDATA[P -> B]]></c>
where <c><![CDATA[P]]></c> is a pattern and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,[Rep(P)],[],Rep(B)}]]></c>.</item>
<item>If C is a case clause <c><![CDATA[P when Gs -> B]]></c>
where <c><![CDATA[P]]></c> is a pattern,
<c><![CDATA[Gs]]></c> is a guard sequence and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,[Rep(P)],Rep(Gs),Rep(B)}]]></c>.</item>
<item>If C is a catch clause <c><![CDATA[P -> B]]></c>
where <c><![CDATA[P]]></c> is a pattern and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,[Rep({throw,P,_})],[],Rep(B)}]]></c>.</item>
<item>If C is a catch clause <c><![CDATA[X : P -> B]]></c>
where <c><![CDATA[X]]></c> is an atomic literal or a variable pattern,
<c><![CDATA[P]]></c> is a pattern and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,[Rep({X,P,_})],[],Rep(B)}]]></c>.</item>
<item>If C is a catch clause <c><![CDATA[P when Gs -> B]]></c>
where <c><![CDATA[P]]></c> is a pattern, <c><![CDATA[Gs]]></c> is a guard sequence
and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,[Rep({throw,P,_})],Rep(Gs),Rep(B)}]]></c>.</item>
<item>If C is a catch clause <c><![CDATA[X : P when Gs -> B]]></c>
where <c><![CDATA[X]]></c> is an atomic literal or a variable pattern,
<c><![CDATA[P]]></c> is a pattern, <c><![CDATA[Gs]]></c> is a guard sequence
and <c><![CDATA[B]]></c> is a body, then
Rep(C) = <c><![CDATA[{clause,LINE,[Rep({X,P,_})],Rep(Gs),Rep(B)}]]></c>.</item>
</list>
</section>
<section>
<title>Guards</title>
<p>A guard sequence Gs is a sequence of guards <c><![CDATA[G_1; ...; G_k]]></c>, and
Rep(Gs) = <c><![CDATA[[Rep(G_1), ..., Rep(G_k)]]]></c>. If the guard sequence is
empty, Rep(Gs) = <c><![CDATA[[]]]></c>.</p>
<p>A guard G is a nonempty sequence of guard tests <c><![CDATA[Gt_1, ..., Gt_k]]></c>, and
Rep(G) = <c><![CDATA[[Rep(Gt_1), ..., Rep(Gt_k)]]]></c>.</p>
<p>A guard test <c><![CDATA[Gt]]></c> is one of the following alternatives:</p>
<list type="bulleted">
<item>If Gt is an atomic literal L, then Rep(Gt) = Rep(L).</item>
<item>If Gt is a variable pattern <c><![CDATA[V]]></c>, then
Rep(Gt) = <c><![CDATA[{var,LINE,A}]]></c>,
where A is an atom with a printname consisting of the same characters as
<c><![CDATA[V]]></c>.</item>
<item>If Gt is a tuple skeleton <c><![CDATA[{Gt_1, ..., Gt_k}]]></c>, then
Rep(Gt) = <c><![CDATA[{tuple,LINE,[Rep(Gt_1), ..., Rep(Gt_k)]}]]></c>.</item>
<item>If Gt is <c><![CDATA[[]]]></c>, then
Rep(Gt) = <c><![CDATA[{nil,LINE}]]></c>.</item>
<item>If Gt is a cons skeleton <c><![CDATA[[Gt_h | Gt_t]]]></c>, then
Rep(Gt) = <c><![CDATA[{cons,LINE,Rep(Gt_h),Rep(Gt_t)}]]></c>.</item>
<item>If Gt is a binary constructor <c><![CDATA[<<Gt_1:Size_1/TSL_1, ..., Gt_k:Size_k/TSL_k>>]]></c>, then
Rep(Gt) = <c><![CDATA[{bin,LINE,[{bin_element,LINE,Rep(Gt_1),Rep(Size_1),Rep(TSL_1)}, ..., {bin_element,LINE,Rep(Gt_k),Rep(Size_k),Rep(TSL_k)}]}]]></c>.
For Rep(TSL), see above.
An omitted <c><![CDATA[Size]]></c> is represented by <c><![CDATA[default]]></c>. An omitted <c><![CDATA[TSL]]></c>
(type specifier list) is represented by <c><![CDATA[default]]></c>.</item>
<item>If Gt is <c><![CDATA[Gt_1 Op Gt_2]]></c>, where <c><![CDATA[Op]]></c>
is a binary operator, then Rep(Gt) = <c><![CDATA[{op,LINE,Op,Rep(Gt_1),Rep(Gt_2)}]]></c>.</item>
<item>If Gt is <c><![CDATA[Op Gt_0]]></c>, where <c><![CDATA[Op]]></c> is a unary operator, then
Rep(Gt) = <c><![CDATA[{op,LINE,Op,Rep(Gt_0)}]]></c>.</item>
<item>If Gt is <c><![CDATA[#Name{Field_1=Gt_1, ..., Field_k=Gt_k}]]></c>, then
Rep(E) =
<c><![CDATA[{record,LINE,Name, [{record_field,LINE,Rep(Field_1),Rep(Gt_1)}, ..., {record_field,LINE,Rep(Field_k),Rep(Gt_k)}]}]]></c>.</item>
<item>If Gt is <c><![CDATA[#Name.Field]]></c>, then
Rep(Gt) = <c><![CDATA[{record_index,LINE,Name,Rep(Field)}]]></c>.</item>
<item>If Gt is <c><![CDATA[Gt_0#Name.Field]]></c>, then
Rep(Gt) = <c><![CDATA[{record_field,LINE,Rep(Gt_0),Name,Rep(Field)}]]></c>.</item>
<item>If Gt is <c><![CDATA[A(Gt_1, ..., Gt_k)]]></c>, where <c><![CDATA[A]]></c> is an atom, then
Rep(Gt) = <c><![CDATA[{call,LINE,Rep(A),[Rep(Gt_1), ..., Rep(Gt_k)]}]]></c>.</item>
<item>If Gt is <c><![CDATA[A_m:A(Gt_1, ..., Gt_k)]]></c>, where <c><![CDATA[A_m]]></c> is
the atom <c><![CDATA[erlang]]></c> and <c><![CDATA[A]]></c> is an atom or an operator, then
Rep(Gt) = <c><![CDATA[{call,LINE,{remote,LINE,Rep(A_m),Rep(A)},[Rep(Gt_1), ..., Rep(Gt_k)]}]]></c>.</item>
<item>If Gt is <c><![CDATA[{A_m,A}(Gt_1, ..., Gt_k)]]></c>, where <c><![CDATA[A_m]]></c> is
the atom <c><![CDATA[erlang]]></c> and <c><![CDATA[A]]></c> is an atom or an operator, then
Rep(Gt) = <c><![CDATA[{call,LINE,Rep({A_m,A}),[Rep(Gt_1), ..., Rep(Gt_k)]}]]></c>.</item>
<item>If Gt is <c><![CDATA[( Gt_0 )]]></c>, then
Rep(Gt) = <c><![CDATA[Rep(Gt_0)]]></c>,
i.e., parenthesized guard tests cannot be distinguished from their bodies.</item>
</list>
<p>Note that every guard test has the same source form as some expression,
and is represented the same way as the corresponding expression.</p>
</section>
<section>
<title>The abstract format after preprocessing</title>
<p>The compilation option <c><![CDATA[debug_info]]></c> can be given to the
compiler to have the abstract code stored in
the <c><![CDATA[abstract_code]]></c> chunk in the BEAM file
(for debugging purposes).</p>
<p>In OTP R9C and later, the <c><![CDATA[abstract_code]]></c> chunk will
contain</p>
<p><c><![CDATA[{raw_abstract_v1,AbstractCode}]]></c></p>
<p>where <c><![CDATA[AbstractCode]]></c> is the abstract code as described
in this document.</p>
<p>In releases of OTP prior to R9C, the abstract code after some more
processing was stored in the BEAM file. The first element of the
tuple would be either <c><![CDATA[abstract_v1]]></c> (R7B) or <c><![CDATA[abstract_v2]]></c>
(R8B).</p>
</section>
</chapter>
