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<header>
<copyright>
<year>2001</year><year>2015</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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<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 type attribute (i.e. <c><![CDATA[opaque]]></c> or
<c><![CDATA[type]]></c>)
<c><![CDATA[-Attr Name(A_1, ..., A_k) :: T]]></c> where each
<c><![CDATA[A_i]]></c> is a variable, then Rep(F) =
<c><![CDATA[{attribute,LINE,Attr,{Name,Rep(T),[Rep(A_1), ..., Rep(A_k)]}}]]></c>.
For Rep(T), see below.</item>
<item>If F is a type spec (i.e. <c><![CDATA[callback]]></c> or
<c><![CDATA[spec]]></c>)
<c><![CDATA[-Attr F Tc_1; ...; Tc_k]]></c>,
where each <c><![CDATA[Tc_i]]></c> is a fun type clause with an
argument sequence of the same length <c><![CDATA[Arity]]></c>, then
Rep(F) =
<c><![CDATA[{Attr,LINE,{{F,Arity},[Rep(Tc_1), ..., Rep(Tc_k)]}}]]></c>.
For Rep(Tc_i), see below.</item>
<item>If F is a type spec (i.e. <c><![CDATA[callback]]></c> or
<c><![CDATA[spec]]></c>)
<c><![CDATA[-Attr Mod:F Tc_1; ...; Tc_k]]></c>,
where each <c><![CDATA[Tc_i]]></c> is a fun type clause with an
argument sequence of the same length <c><![CDATA[Arity]]></c>, then
Rep(F) =
<c><![CDATA[{Attr,LINE,{{Mod,F,Arity},[Rep(Tc_1), ..., Rep(Tc_k)]}}]]></c>.
For Rep(Tc_i), 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>Type clauses</title>
<list type="bulleted">
<item>If T is a fun type clause
<c><![CDATA[(A_1, ..., A_n) -> Ret]]></c>, where each
<c><![CDATA[A_i]]></c> and <c><![CDATA[Ret]]></c> are types, then
Rep(T) =
<c><![CDATA[{type,LINE,'fun',[{type,LINE,product,[Rep(A_1), ..., Rep(A_n)]},Rep(Ret)]}]]></c>.
</item>
<item>If T is a bounded fun type clause <c><![CDATA[Tc when Tg]]></c>,
where <c><![CDATA[Tc]]></c> is an unbounded fun type clause and
<c><![CDATA[Tg]]></c> is a type guard sequence, then Rep(T) =
<c><![CDATA[{type,LINE,bounded_fun,[Rep(Tc),Rep(Tg)]}]]></c>.</item>
</list>
</section>
<section>
<title>Type guards</title>
<list type="bulleted">
<item>If G is a constraint <c><![CDATA[F(A_1, ..., A_k)]]></c>, where
<c><![CDATA[F]]></c> is an atom and each <c><![CDATA[A_i]]></c> is a
type, then Rep(G) =
<c><![CDATA[{type,LINE,constraint,[Rep(F),[Rep(A_1), ..., Rep(A_k)]]}]]></c>.
</item>
<item>If G is a type definition <c><![CDATA[Name :: Type]]></c>,
where <c><![CDATA[Name]]></c> is a variable and
<c><![CDATA[Type]]></c> is a type, then Rep(G) =
<c><![CDATA[{type,LINE,constraint,[{atom,LINE,is_subtype},[Rep(Name),Rep(Type)]]}]]></c>.</item>
</list>
</section>
<section>
<title>Types</title>
<list type="bulleted">
<item>If T is a type definition <c><![CDATA[Name :: Type]]></c>,
where <c><![CDATA[Name]]></c> is a variable and
<c><![CDATA[Type]]></c> is a type, then Rep(T) =
<c><![CDATA[{ann_type,LINE,[Rep(Name),Rep(Type)]}]]></c>.</item>
<item>If T is a type union <c><![CDATA[A_1 | ... | A_k]]></c>,
where each <c><![CDATA[A_i]]></c> is a type, then Rep(T) =
<c><![CDATA[{type,LINE,union,[Rep(A_1), ..., Rep(A_k)]}]]></c>.</item>
<item>If T is a type range <c><![CDATA[L .. R]]></c>,
where <c><![CDATA[L]]></c> and <c><![CDATA[R]]></c> are types, then
Rep(T) = <c><![CDATA[{type,LINE,range,[Rep(L), Rep(R)]}]]></c>.</item>
<item>If T is a binary operation <c><![CDATA[L Op R]]></c>,
where <c><![CDATA[Op]]></c> is an arithmetic or bitwise binary operator
and <c><![CDATA[L]]></c> and <c><![CDATA[R]]></c> are types, then
Rep(T) = <c><![CDATA[{op,LINE,Op,Rep(L),Rep(R)}]]></c>.</item>
<item>If T is <c><![CDATA[Op A]]></c>, where <c><![CDATA[Op]]></c> is an
arithmetic or bitwise unary operator and <c><![CDATA[A]]></c> is a
type, then Rep(T) = <c><![CDATA[{op,LINE,Op,Rep(A)}]]></c>.</item>
<item>If T is a fun type <c><![CDATA[fun()]]></c>, then Rep(T) =
<c><![CDATA[{type,LINE,'fun',[]}]]></c>.</item>
<item>If T is a variable <c><![CDATA[V]]></c>, then Rep(T) =
<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 T is an atomic literal L and L is not a string literal, then
Rep(T) = Rep(L).</item>
<item>If T is a tuple or map type <c><![CDATA[F()]]></c> (i.e.
<c><![CDATA[tuple]]></c> or <c><![CDATA[map]]></c>), then Rep(T) =
<c><![CDATA[{type,LINE,F,any}]]></c>.</item>
<item>If T is a type <c><![CDATA[F(A_1, ..., A_k)]]></c>, where each
<c><![CDATA[A_i]]></c> is a type, then Rep(T) =
<c><![CDATA[{user_type,LINE,F,[Rep(A_1), ..., Rep(A_k)]}]]></c>.</item>
<item>If T is a remote type <c><![CDATA[M:F(A_1, ..., A_k)]]></c>, where
each <c><![CDATA[A_i]]></c> is a type and <c><![CDATA[M]]></c> and
<c><![CDATA[F]]></c>, then Rep(T) =
<c><![CDATA[{remote_type,LINE,[Rep(M),Rep(F),[Rep(A_1), ..., Rep(A_k)]]}]]></c>.
</item>
<item>If T is the nil type <c><![CDATA[[]]]></c>, then Rep(T) =
<c><![CDATA[{type,LINE,nil,[]}]]></c>.</item>
<item>If T is a list type <c><![CDATA[[A]]]></c>, where
<c><![CDATA[A]]></c> is a type, then Rep(T) =
<c><![CDATA[{type,LINE,list,[Rep(A)]}]]></c>.</item>
<item>If T is a non-empty list type <c><![CDATA[[A, ...]]]></c>, where
<c><![CDATA[A]]></c> is a type, then Rep(T) =
<c><![CDATA[{type,LINE,nonempty_list,[Rep(A)]}]]></c>.</item>
<item>If T is a map type <c><![CDATA[#{P_1, ..., P_k}]]></c>, where each
<c><![CDATA[P_i]]></c> is a map pair type, then Rep(T) =
<c><![CDATA[{type,LINE,map,[Rep(P_1), ..., Rep(P_k)]}]]></c>.</item>
<item>If T is a map pair type <c><![CDATA[K => V]]></c>, where
<c><![CDATA[K]]></c> and <c><![CDATA[V]]></c> are types,
then Rep(T) =
<c><![CDATA[{type,LINE,map_field_assoc,[Rep(K),Rep(V)]}]]></c>.</item>
<item>If T is a tuple type <c><![CDATA[{A_1, ..., A_k}]]></c>, where
each <c><![CDATA[A_i]]></c> is a type, then Rep(T) =
<c><![CDATA[{type,LINE,tuple,[Rep(A_1), ..., Rep(A_k)]}]]></c>.</item>
<item>If T is a record type <c><![CDATA[#Name{}]]></c>, where
<c><![CDATA[Name]]></c> is an atom, then Rep(T) =
<c><![CDATA[{type,LINE,record,[Rep(Name)]}]]></c>.</item>
<item>If T is a record type <c><![CDATA[#Name{F_1, ..., F_k}]]></c>,
where <c><![CDATA[Name]]></c> is an atom, then Rep(T) =
<c><![CDATA[{type,LINE,record,[Rep(Name),[Rep(F_1), ..., Rep(F_k)]]}]]></c>.
</item>
<item>If T is a record field type <c><![CDATA[Name :: Type]]></c>,
where <c><![CDATA[Name]]></c> is an atom, then Rep(T) =
<c><![CDATA[{type,LINE,field_type,[Rep(Name),Rep(Type)]}]]></c>.</item>
<item>If T is a record field type <c><![CDATA[<<>>]]></c>, then Rep(T) =
<c><![CDATA[{type,LINE,binary,[{integer,LINE,0},{integer,LINE,0}]}]]></c>.
</item>
<item>If T is a binary type <c><![CDATA[<< _ : B >>]]></c>, where
<c><![CDATA[B]]></c> is a type, then Rep(T) =
<c><![CDATA[{type,LINE,binary,[Rep(B),{integer,LINE,0}]}]]></c>.</item>
<item>If T is a binary type <c><![CDATA[<< _ : _ * U >>]]></c>,
where <c><![CDATA[U]]></c> is a type, then Rep(T) =
<c><![CDATA[{type,LINE,binary,[{integer,LINE,0},Rep(U)]}]]></c>.</item>
<item>If T is a binary type <c><![CDATA[<< _ : B , _ : _ * U >>]]></c>,
where <c><![CDATA[B]]></c> and <c><![CDATA[U]]></c> is a type, then
Rep(T) =
<c><![CDATA[{type,LINE,binary,[Rep(B),Rep(U)]}]]></c>.</item>
<item>If T is a fun type <c><![CDATA[fun((...) -> Ret)]]></c>, then
Rep(T) = <c><![CDATA[{type,LINE,'fun',[{type,LINE,product,[]},Rep(Ret)]}]]></c>.
</item>
<item>If T is a fun type <c><![CDATA[fun(Tc)]]></c>, where
<c><![CDATA[Tc]]></c> is an unbounded fun type clause,
then Rep(T) = <c><![CDATA[Rep(Tc)]]></c>.</item>
</list>
</section>
<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>
<item>If V is <c><![CDATA[A :: T]]></c>, where <c><![CDATA[A]]></c> is
an atom and <c><![CDATA[T]]></c> is a type and it does not contain
<c><![CDATA[undefined]]></c> syntactically, then Rep(V) =
<c><![CDATA[{typed_record_field,{record_field,LINE,Rep(A)},Rep(undefined | T)}]]></c>.
Note that if <![CDATA[T]]> is an annotated type, it will be wrapped in
parentheses.</item>
<item>If V is <c><![CDATA[A :: T]]></c>, where <c><![CDATA[A]]></c> is
an atom and <c><![CDATA[T]]></c> is a type, then Rep(V) =
<c><![CDATA[{typed_record_field,{record_field,LINE,Rep(A)},Rep(T)}]]></c>.
</item>
<item>If V is <c><![CDATA[A = E :: T]]></c>, where <c><![CDATA[A]]></c>
is an atom, <c><![CDATA[E]]></c> is an expression and
<c><![CDATA[T]]></c> is a type, then Rep(V) =
<c><![CDATA[{typed_record_field,{record_field,LINE,Rep(A),Rep(E)},Rep(T)}]]></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[#{W_1, ..., W_k}]]></c> where each
<c><![CDATA[W_i]]></c> is a map assoc or exact field, then Rep(E) =
<c><![CDATA[{map,LINE,[Rep(W_1), ..., Rep(W_k)]}]]></c>. For Rep(W), see
below.</item>
<item>If E is <c><![CDATA[E_0#{W_1, ..., W_k}]]></c> where
<c><![CDATA[W_i]]></c> is a map assoc or exact field, then Rep(E) =
<c><![CDATA[{map,LINE,Rep(E_0),[Rep(W_1), ..., Rep(W_k)]}]]></c>. For
Rep(W), see below.</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[fun Name Fc_1 ; ... ; Name Fc_k end]]></c>
where <c><![CDATA[Name]]></c> is a variable and each
<c><![CDATA[Fc_i]]></c> is a function clause then Rep(E) =
<c><![CDATA[{named_fun,LINE,Name,[Rep(Fc_1), ..., Rep(Fc_k)]}]]></c>.
</item>
<item>If E is <c><![CDATA[query [E_0 || W_1, ..., W_k] end]]></c>,
where each <c><![CDATA[W_i]]></c> is a generator or a filter, then
Rep(E) = <c><![CDATA[{'query',LINE,{lc,LINE,Rep(E_0),[Rep(W_1), ..., Rep(W_k)]}}]]></c>.
For Rep(W), see below.</item>
<item>If E is <c><![CDATA[E_0.Field]]></c>, a Mnesia record access
inside a query, then
Rep(E) = <c><![CDATA[{record_field,LINE,Rep(E_0),Rep(Field)}]]></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>
<title>Map assoc and exact fields</title>
<p>When W is an assoc or exact field (in the body of a map), then:</p>
<list type="bulleted">
<item>If W is an assoc field <c><![CDATA[K => V]]></c>, where
<c><![CDATA[K]]></c> and <c><![CDATA[V]]></c> are both expressions,
then Rep(W) = <c><![CDATA[{map_field_assoc,LINE,Rep(K),Rep(V)}]]></c>.
</item>
<item>If W is an exact field <c><![CDATA[K := V]]></c>, where
<c><![CDATA[K]]></c> and <c><![CDATA[V]]></c> are both expressions,
then Rep(W) = <c><![CDATA[{map_field_exact,LINE,Rep(K),Rep(V)}]]></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>
