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<header>
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<year>2001</year><year>2016</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
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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>compile:forms/[1,2]</c>
and functions in the modules
<c>epp</c>,
<c>erl_eval</c>,
<c>erl_lint</c>,
<c>erl_pp</c>,
<c>erl_parse</c>,
and
<c>io</c>.
They are also used as input and output for parse transforms (see the module
<c>compile</c>).</p>
<p>We use the function <c>Rep</c> to denote the mapping from an Erlang source
construct <c>C</c> to its abstract format representation <c>R</c>, and write
<c>R = Rep(C)</c>.
</p>
<p>The word <c>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>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>F_1</c>, ..., <c>F_k</c>, then
Rep(D) = <c>[Rep(F_1), ..., Rep(F_k)]</c>.</item>
<item>If F is an attribute <c>-export([Fun_1/A_1, ..., Fun_k/A_k])</c>, then
Rep(F) = <c>{attribute,LINE,export,[{Fun_1,A_1}, ..., {Fun_k,A_k}]}</c>.</item>
<item>If F is an attribute <c>-import(Mod,[Fun_1/A_1, ..., Fun_k/A_k])</c>, then
Rep(F) = <c>{attribute,LINE,import,{Mod,[{Fun_1,A_1}, ..., {Fun_k,A_k}]}}</c>.</item>
<item>If F is an attribute <c>-module(Mod)</c>, then
Rep(F) = <c>{attribute,LINE,module,Mod}</c>.</item>
<item>If F is an attribute <c>-file(File,Line)</c>, then
Rep(F) = <c>{attribute,LINE,file,{File,Line}}</c>.</item>
<item>If F is a function declaration
<c>Name Fc_1 ; ... ; Name Fc_k</c>,
where each <c>Fc_i</c> is a function clause with a
pattern sequence of the same length <c>Arity</c>, then
Rep(F) = <c>{function,LINE,Name,Arity,[Rep(Fc_1), ...,Rep(Fc_k)]}</c>.
</item>
<item>If F is a function specification
<c>-Spec Name Ft_1; ...; Ft_k</c>,
where <c>Spec</c> is either the atom <c>spec</c> or the atom
<c>callback</c>, and each <c>Ft_i</c> is a possibly constrained
function type with an argument sequence of the same length
<c>Arity</c>, then Rep(F) =
<c>{attribute,Line,Spec,{{Name,Arity},[Rep(Ft_1), ..., Rep(Ft_k)]}}</c>.
</item>
<item>If F is a function specification
<c>-spec Mod:Name Ft_1; ...; Ft_k</c>,
where each <c>Ft_i</c> is a possibly constrained
function type with an argument sequence of the same length
<c>Arity</c>, then Rep(F) =
<c>{attribute,Line,spec,{{Mod,Name,Arity},[Rep(Ft_1), ..., Rep(Ft_k)]}}</c>.
</item>
<item>If F is a record declaration
<c>-record(Name,{V_1, ..., V_k})</c>,
where each <c>V_i</c> is a record field, then Rep(F) =
<c>{attribute,LINE,record,{Name,[Rep(V_1), ..., Rep(V_k)]}}</c>.
For Rep(V), see below.</item>
<item>If F is a type declaration
<c>-Type Name(V_1, ..., V_k) :: T</c>, where
<c>Type</c> is either the atom <c>type</c> or the atom <c>opaque</c>,
each <c>V_i</c> is a variable, and <c>T</c> is a type, then Rep(F) =
<c>{attribute,LINE,Type,{Name,Rep(T),[Rep(V_1), ..., Rep(V_k)]}}</c>.
</item>
<item>If F is a wild attribute <c>-A(T)</c>, then
Rep(F) = <c>{attribute,LINE,A,T}</c>.
<br></br></item>
</list>
<section>
<title>Record Fields</title>
<p>Each field in a record declaration may have an optional
explicit default initializer expression, as well as an
optional type.</p>
<list type="bulleted">
<item>If V is <c>A</c>, then
Rep(V) = <c>{record_field,LINE,Rep(A)}</c>.</item>
<item>If V is <c>A = E</c>,
where <c>E</c> is an expression, then
Rep(V) = <c>{record_field,LINE,Rep(A),Rep(E)}</c>.</item>
<item>If V is <c>A :: T</c>, where <c>T</c> is a type, then Rep(V) =
<c>{typed_record_field,{record_field,LINE,Rep(A)},Rep(T)}</c>.
</item>
<item>If V is <c>A = E :: T</c>, where
<c>E</c> is an expression and <c>T</c> is a type, then Rep(V) =
<c>{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>erl_parse</c> and
<c>epp</c>) may contain tuples <c>{error,E}</c> and
<c>{warning,W}</c>, denoting syntactically incorrect forms and
warnings, and <c>{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 atom literal, then
Rep(L) = <c>{atom,LINE,L}</c>.</item>
<item>If L is a character literal, then
Rep(L) = <c>{char,LINE,L}</c>.</item>
<item>If L is a float literal, then
Rep(L) = <c>{float,LINE,L}</c>.</item>
<item>If L is an integer literal, then
Rep(L) = <c>{integer,LINE,L}</c>.</item>
<item>If L is a string literal consisting of the characters
<c>C_1</c>, ..., <c>C_k</c>, then
Rep(L) = <c>{string,LINE,[C_1, ..., C_k]}</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 Ps is a sequence of patterns <c>P_1, ..., P_k</c>, then
Rep(Ps) = <c>[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 <c>L</c>, then Rep(P) = Rep(L).</item>
<item>If P is a bit string pattern
<c><<P_1:Size_1/TSL_1, ..., P_k:Size_k/TSL_k>></c>, where each
<c>Size_i</c> is an expression that can be evaluated to an integer
and each <c>TSL_i</c> is a type specificer list, then
Rep(P) = <c>{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>Size_i</c> is represented by <c>default</c>.
An omitted <c>TSL_i</c> is represented by <c>default</c>.</item>
<item>If P is a compound pattern <c>P_1 = P_2</c>, then
Rep(P) = <c>{match,LINE,Rep(P_1),Rep(P_2)}</c>.</item>
<item>If P is a cons pattern <c>[P_h | P_t]</c>, then
Rep(P) = <c>{cons,LINE,Rep(P_h),Rep(P_t)}</c>.</item>
<item>If P is a map pattern <c>#{A_1, ..., A_k}</c>, where each
<c>A_i</c> is an association <c>P_i_1 := P_i_2</c>, then Rep(P) =
<c>{map,LINE,[Rep(A_1), ..., Rep(A_k)]}</c>. For Rep(A), see
below.</item>
<item>If P is a nil pattern <c>[]</c>, then
Rep(P) = <c>{nil,LINE}</c>.</item>
<item>If P is an operator pattern <c>P_1 Op P_2</c>,
where <c>Op</c> is a binary operator (this is either an occurrence
of <c>++</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>{op,LINE,Op,Rep(P_1),Rep(P_2)}</c>.</item>
<item>If P is an operator pattern <c>Op P_0</c>,
where <c>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>{op,LINE,Op,Rep(P_0)}</c>.</item>
<item>If P is a parenthesized pattern <c>( P_0 )</c>, then
Rep(P) = <c>Rep(P_0)</c>,
that is, parenthesized patterns cannot be distinguished from their
bodies.</item>
<item>If P is a record field index pattern <c>#Name.Field</c>,
where <c>Field</c> is an atom, then
Rep(P) = <c>{record_index,LINE,Name,Rep(Field)}</c>.</item>
<item>If P is a record pattern
<c>#Name{Field_1=P_1, ..., Field_k=P_k}</c>,
where each <c>Field_i</c> is an atom or <c>_</c>, then Rep(P) =
<c>{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 a tuple pattern <c>{P_1, ..., P_k}</c>, then
Rep(P) = <c>{tuple,LINE,[Rep(P_1), ..., Rep(P_k)]}</c>.</item>
<item>If P is a universal pattern <c>_</c>, then
Rep(P) = <c>{var,LINE,'_'}</c>.</item>
<item>If P is a variable pattern <c>V</c>, then
Rep(P) = <c>{var,LINE,A}</c>,
where A is an atom with a printname consisting of the same characters as
<c>V</c>.</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 nonempty sequence of expressions <c>E_1, ..., E_k</c>,
and Rep(B) = <c>[Rep(E_1), ..., Rep(E_k)]</c>.</p>
<p>An expression E is one of the following alternatives:</p>
<list type="bulleted">
<item>If E is an atomic literal <c>L</c>, then Rep(E) = Rep(L).</item>
<item>If E is a bit string comprehension
<c><<E_0 || Q_1, ..., Q_k>></c>,
where each <c>Q_i</c> is a qualifier, then
Rep(E) = <c>{bc,LINE,Rep(E_0),[Rep(Q_1), ..., Rep(Q_k)]}</c>.
For Rep(Q), see below.</item>
<item>If E is a bit string constructor
<c><<E_1:Size_1/TSL_1, ..., E_k:Size_k/TSL_k>></c>,
where each <c>Size_i</c> is an expression and each
<c>TSL_i</c> is a type specificer list, then Rep(E) =
<c>{bin,LINE,[{bin_element,LINE,Rep(E_1),Rep(Size_1),Rep(TSL_1)}, ..., {bin_element,LINE,Rep(E_k),Rep(Size_k),Rep(TSL_k)}]}</c>.
For Rep(TSL), see below.
An omitted <c>Size_i</c> is represented by <c>default</c>.
An omitted <c>TSL_i</c> is represented by <c>default</c>.</item>
<item>If E is a block expression <c>begin B end</c>,
where <c>B</c> is a body, then
Rep(E) = <c>{block,LINE,Rep(B)}</c>.</item>
<item>If E is a case expression <c>case E_0 of Cc_1 ; ... ; Cc_k end</c>,
where <c>E_0</c> is an expression and each <c>Cc_i</c> is a
case clause then Rep(E) =
<c>{'case',LINE,Rep(E_0),[Rep(Cc_1), ..., Rep(Cc_k)]}</c>.</item>
<item>If E is a catch expression <c>catch E_0</c>, then
Rep(E) = <c>{'catch',LINE,Rep(E_0)}</c>.</item>
<item>If E is a cons skeleton <c>[E_h | E_t]</c>, then
Rep(E) = <c>{cons,LINE,Rep(E_h),Rep(E_t)}</c>.</item>
<item>If E is a fun expression <c>fun Name/Arity</c>, then
Rep(E) = <c>{'fun',LINE,{function,Name,Arity}}</c>.</item>
<item>If E is a fun expression
<c>fun Module:Name/Arity</c>, then Rep(E) =
<c>{'fun',LINE,{function,Rep(Module),Rep(Name),Rep(Arity)}}</c>.
(Before the R15 release: Rep(E) =
<c>{'fun',LINE,{function,Module,Name,Arity}}</c>.)</item>
<item>If E is a fun expression <c>fun Fc_1 ; ... ; Fc_k end</c>,
where each <c>Fc_i</c> is a function clause then Rep(E) =
<c>{'fun',LINE,{clauses,[Rep(Fc_1), ..., Rep(Fc_k)]}}</c>.</item>
<item>If E is a fun expression
<c>fun Name Fc_1 ; ... ; Name Fc_k end</c>,
where <c>Name</c> is a variable and each
<c>Fc_i</c> is a function clause then Rep(E) =
<c>{named_fun,LINE,Name,[Rep(Fc_1), ..., Rep(Fc_k)]}</c>.
</item>
<item>If E is a function call <c>E_0(E_1, ..., E_k)</c>, then
Rep(E) = <c>{call,LINE,Rep(E_0),[Rep(E_1), ..., Rep(E_k)]}</c>.</item>
<item>If E is a function call <c>E_m:E_0(E_1, ..., E_k)</c>,
then Rep(E) =
<c>{call,LINE,{remote,LINE,Rep(E_m),Rep(E_0)},[Rep(E_1), ..., Rep(E_k)]}</c>.
</item>
<item>If E is an if expression <c>if Ic_1 ; ... ; Ic_k end</c>,
where each <c>Ic_i</c> is an if clause then Rep(E) =
<c>{'if',LINE,[Rep(Ic_1), ..., Rep(Ic_k)]}</c>.</item>
<item>If E is a list comprehension <c>[E_0 || Q_1, ..., Q_k]</c>,
where each <c>Q_i</c> is a qualifier, then Rep(E) =
<c>{lc,LINE,Rep(E_0),[Rep(Q_1), ..., Rep(Q_k)]}</c>. For Rep(Q), see
below.</item>
<item>If E is a map creation <c>#{A_1, ..., A_k}</c>,
where each <c>A_i</c> is an association <c>E_i_1 => E_i_2</c>
or <c>E_i_1 := E_i_2</c>, then Rep(E) =
<c>{map,LINE,[Rep(A_1), ..., Rep(A_k)]}</c>. For Rep(A), see
below.</item>
<item>If E is a map update <c>E_0#{A_1, ..., A_k}</c>,
where each <c>A_i</c> is an association <c>E_i_1 => E_i_2</c>
or <c>E_i_1 := E_i_2</c>, then Rep(E) =
<c>{map,LINE,Rep(E_0),[Rep(A_1), ..., Rep(A_k)]}</c>.
For Rep(A), see below.</item>
<item>If E is a match operator expression <c>P = E_0</c>,
where <c>P</c> is a pattern, then
Rep(E) = <c>{match,LINE,Rep(P),Rep(E_0)}</c>.</item>
<item>If E is nil, <c>[]</c>, then
Rep(E) = <c>{nil,LINE}</c>.</item>
<item>If E is an operator expression <c>E_1 Op E_2</c>,
where <c>Op</c> is a binary operator other than the match
operator <c>=</c>, then
Rep(E) = <c>{op,LINE,Op,Rep(E_1),Rep(E_2)}</c>.</item>
<item>If E is an operator expression <c>Op E_0</c>,
where <c>Op</c> is a unary operator, then
Rep(E) = <c>{op,LINE,Op,Rep(E_0)}</c>.</item>
<item>If E is a parenthesized expression <c>( E_0 )</c>, then
Rep(E) = <c>Rep(E_0)</c>, that is, parenthesized
expressions cannot be distinguished from their bodies.</item>
<item>If E is a receive expression <c>receive Cc_1 ; ... ; Cc_k end</c>,
where each <c>Cc_i</c> is a case clause then Rep(E) =
<c>{'receive',LINE,[Rep(Cc_1), ..., Rep(Cc_k)]}</c>.</item>
<item>If E is a receive expression
<c>receive Cc_1 ; ... ; Cc_k after E_0 -> B_t end</c>,
where each <c>Cc_i</c> is a case clause,
<c>E_0</c> is an expression and <c>B_t</c> is a body, then Rep(E) =
<c>{'receive',LINE,[Rep(Cc_1), ..., Rep(Cc_k)],Rep(E_0),Rep(B_t)}</c>.</item>
<item>If E is a record creation
<c>#Name{Field_1=E_1, ..., Field_k=E_k}</c>,
where each <c>Field_i</c> is an atom or <c>_</c>, then Rep(E) =
<c>{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 a record field access <c>E_0#Name.Field</c>,
where <c>Field</c> is an atom, then
Rep(E) = <c>{record_field,LINE,Rep(E_0),Name,Rep(Field)}</c>.</item>
<item>If E is a record field index <c>#Name.Field</c>,
where <c>Field</c> is an atom, then
Rep(E) = <c>{record_index,LINE,Name,Rep(Field)}</c>.</item>
<item>If E is a record update
<c>E_0#Name{Field_1=E_1, ..., Field_k=E_k}</c>,
where each <c>Field_i</c> is an atom, then Rep(E) =
<c>{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 a tuple skeleton <c>{E_1, ..., E_k}</c>, then
Rep(E) = <c>{tuple,LINE,[Rep(E_1), ..., Rep(E_k)]}</c>.</item>
<item>If E is a try expression <c>try B catch Tc_1 ; ... ; Tc_k end</c>,
where <c>B</c> is a body and each <c>Tc_i</c> is a catch clause then
Rep(E) =
<c>{'try',LINE,Rep(B),[],[Rep(Tc_1), ..., Rep(Tc_k)],[]}</c>.</item>
<item>If E is a try expression
<c>try B of Cc_1 ; ... ; Cc_k catch Tc_1 ; ... ; Tc_n end</c>,
where <c>B</c> is a body,
each <c>Cc_i</c> is a case clause and
each <c>Tc_j</c> is a catch clause then Rep(E) =
<c>{'try',LINE,Rep(B),[Rep(Cc_1), ..., Rep(Cc_k)],[Rep(Tc_1), ..., Rep(Tc_n)],[]}</c>.</item>
<item>If E is a try expression <c>try B after A end</c>,
where <c>B</c> and <c>A</c> are bodies then Rep(E) =
<c>{'try',LINE,Rep(B),[],[],Rep(A)}</c>.</item>
<item>If E is a try expression
<c>try B of Cc_1 ; ... ; Cc_k after A end</c>,
where <c>B</c> and <c>A</c> are a bodies and
each <c>Cc_i</c> is a case clause then Rep(E) =
<c>{'try',LINE,Rep(B),[Rep(Cc_1), ..., Rep(Cc_k)],[],Rep(A)}</c>.</item>
<item>If E is a try expression
<c>try B catch Tc_1 ; ... ; Tc_k after A end</c>,
where <c>B</c> and <c>A</c> are bodies and
each <c>Tc_i</c> is a catch clause then Rep(E) =
<c>{'try',LINE,Rep(B),[],[Rep(Tc_1), ..., Rep(Tc_k)],Rep(A)}</c>.</item>
<item>If E is a try expression
<c>try B of Cc_1 ; ... ; Cc_k catch Tc_1 ; ... ; Tc_n after A end</c>,
where <c>B</c> and <c>A</c> are a bodies,
each <c>Cc_i</c> is a case clause, and
each <c>Tc_j</c> is a catch clause then
Rep(E) =
<c>{'try',LINE,Rep(B),[Rep(Cc_1), ..., Rep(Cc_k)],[Rep(Tc_1), ..., Rep(Tc_n)],Rep(A)}</c>.</item>
<item>If E is a variable <c>V</c>, then Rep(E) = <c>{var,LINE,A}</c>,
where <c>A</c> is an atom with a printname consisting of the same
characters as <c>V</c>.</item>
</list>
<section>
<title>Qualifiers</title>
<p>A qualifier Q is one of the following alternatives:</p>
<list type="bulleted">
<item>If Q is a filter <c>E</c>, where <c>E</c> is an expression, then
Rep(Q) = <c>Rep(E)</c>.</item>
<item>If Q is a generator <c>P <- E</c>, where <c>P</c> is
a pattern and <c>E</c> is an expression, then
Rep(Q) = <c>{generate,LINE,Rep(P),Rep(E)}</c>.</item>
<item>If Q is a bit string generator
<c>P <= E</c>, where <c>P</c> is
a pattern and <c>E</c> is an expression, then
Rep(Q) = <c>{b_generate,LINE,Rep(P),Rep(E)}</c>.</item>
</list>
</section>
<section>
<title>Bit String Element Type Specifiers</title>
<p>A type specifier list TSL for a bit string element is a sequence
of type specifiers <c>TS_1 - ... - TS_k</c>, and
Rep(TSL) = <c>[Rep(TS_1), ..., Rep(TS_k)]</c>.</p>
<list type="bulleted">
<item>If TS is a type specifier <c>A</c>, where <c>A</c> is an atom,
then Rep(TS) = <c>A</c>.</item>
<item>If TS is a type specifier <c>A:Value</c>,
where <c>A</c> is an atom and <c>Value</c> is an integer,
then Rep(TS) = <c>{A,Value}</c>.</item>
</list>
</section>
<section>
<title>Associations</title>
<p>An association A is one of the following alternatives:</p>
<list type="bulleted">
<item>If A is an association <c>K => V</c>,
then Rep(A) = <c>{map_field_assoc,LINE,Rep(K),Rep(V)}</c>.
</item>
<item>If A is an association <c>K := V</c>,
then Rep(A) = <c>{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>C</c> is one of the following alternatives:</p>
<list type="bulleted">
<item>If C is a case clause <c>P -> B</c>,
where <c>P</c> is a pattern and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,[Rep(P)],[],Rep(B)}</c>.</item>
<item>If C is a case clause <c>P when Gs -> B</c>,
where <c>P</c> is a pattern,
<c>Gs</c> is a guard sequence and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,[Rep(P)],Rep(Gs),Rep(B)}</c>.</item>
<item>If C is a catch clause <c>P -> B</c>,
where <c>P</c> is a pattern and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,[Rep({throw,P,_})],[],Rep(B)}</c>.</item>
<item>If C is a catch clause <c>X : P -> B</c>,
where <c>X</c> is an atomic literal or a variable pattern,
<c>P</c> is a pattern, and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,[Rep({X,P,_})],[],Rep(B)}</c>.</item>
<item>If C is a catch clause <c>P when Gs -> B</c>,
where <c>P</c> is a pattern, <c>Gs</c> is a guard sequence,
and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,[Rep({throw,P,_})],Rep(Gs),Rep(B)}</c>.</item>
<item>If C is a catch clause <c>X : P when Gs -> B</c>,
where <c>X</c> is an atomic literal or a variable pattern,
<c>P</c> is a pattern, <c>Gs</c> is a guard sequence,
and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,[Rep({X,P,_})],Rep(Gs),Rep(B)}</c>.</item>
<item>If C is a function clause <c>( Ps ) -> B</c>,
where <c>Ps</c> is a pattern sequence and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,Rep(Ps),[],Rep(B)}</c>.</item>
<item>If C is a function clause <c>( Ps ) when Gs -> B</c>,
where <c>Ps</c> is a pattern sequence,
<c>Gs</c> is a guard sequence and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,Rep(Ps),Rep(Gs),Rep(B)}</c>.</item>
<item>If C is an if clause <c>Gs -> B</c>,
where <c>Gs</c> is a guard sequence and <c>B</c> is a body, then
Rep(C) = <c>{clause,LINE,[],Rep(Gs),Rep(B)}</c>.</item>
</list>
</section>
<section>
<title>Guards</title>
<p>A guard sequence Gs is a sequence of guards <c>G_1; ...; G_k</c>, and
Rep(Gs) = <c>[Rep(G_1), ..., Rep(G_k)]</c>. If the guard sequence is
empty, Rep(Gs) = <c>[]</c>.</p>
<p>A guard G is a nonempty sequence of guard tests
<c>Gt_1, ..., Gt_k</c>, and Rep(G) =
<c>[Rep(Gt_1), ..., Rep(Gt_k)]</c>.</p>
<p>A guard test <c>Gt</c> is one of the following alternatives:</p>
<list type="bulleted">
<item>If Gt is an atomic literal <c>L</c>, then Rep(Gt) = Rep(L).</item>
<item>If Gt is a bit string constructor
<c><<Gt_1:Size_1/TSL_1, ..., Gt_k:Size_k/TSL_k>></c>,
where each <c>Size_i</c> is a guard test and each
<c>TSL_i</c> is a type specificer list, then
Rep(Gt) = <c>{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>Size_i</c> is represented by <c>default</c>.
An omitted <c>TSL_i</c> is represented by <c>default</c>.</item>
<item>If Gt is a cons skeleton <c>[Gt_h | Gt_t]</c>, then
Rep(Gt) = <c>{cons,LINE,Rep(Gt_h),Rep(Gt_t)}</c>.</item>
<item>If Gt is a function call <c>A(Gt_1, ..., Gt_k)</c>,
where <c>A</c> is an atom, then Rep(Gt) =
<c>{call,LINE,Rep(A),[Rep(Gt_1), ..., Rep(Gt_k)]}</c>.</item>
<item>If Gt is a function call <c>A_m:A(Gt_1, ..., Gt_k)</c>,
where <c>A_m</c> is the atom <c>erlang</c> and <c>A</c> is
an atom or an operator, then Rep(Gt) =
<c>{call,LINE,{remote,LINE,Rep(A_m),Rep(A)},[Rep(Gt_1), ..., Rep(Gt_k)]}</c>.</item>
<item>If Gt is a map creation <c>#{A_1, ..., A_k}</c>,
where each <c>A_i</c> is an association <c>Gt_i_1 => Gt_i_2</c>
or <c>Gt_i_1 := Gt_i_2</c>, then Rep(Gt) =
<c>{map,LINE,[Rep(A_1), ..., Rep(A_k)]}</c>. For Rep(A), see
above.</item>
<item>If Gt is a map update <c>Gt_0#{A_1, ..., A_k}</c>, where each
<c>A_i</c> is an association <c>Gt_i_1 => Gt_i_2</c>
or <c>Gt_i_1 := Gt_i_2</c>, then Rep(Gt) =
<c>{map,LINE,Rep(Gt_0),[Rep(A_1), ..., Rep(A_k)]}</c>.
For Rep(A), see above.</item>
<item>If Gt is nil, <c>[]</c>,
then Rep(Gt) = <c>{nil,LINE}</c>.</item>
<item>If Gt is an operator guard test <c>Gt_1 Op Gt_2</c>,
where <c>Op</c> is a binary operator other than the match
operator <c>=</c>, then
Rep(Gt) = <c>{op,LINE,Op,Rep(Gt_1),Rep(Gt_2)}</c>.</item>
<item>If Gt is an operator guard test <c>Op Gt_0</c>,
where <c>Op</c> is a unary operator, then
Rep(Gt) = <c>{op,LINE,Op,Rep(Gt_0)}</c>.</item>
<item>If Gt is a parenthesized guard test <c>( Gt_0 )</c>, then
Rep(Gt) = <c>Rep(Gt_0)</c>, that is, parenthesized
guard tests cannot be distinguished from their bodies.</item>
<item>If Gt is a record creation
<c>#Name{Field_1=Gt_1, ..., Field_k=Gt_k}</c>,
where each <c>Field_i</c> is an atom or <c>_</c>, then Rep(Gt) =
<c>{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 a record field access <c>Gt_0#Name.Field</c>,
where <c>Field</c> is an atom, then
Rep(Gt) = <c>{record_field,LINE,Rep(Gt_0),Name,Rep(Field)}</c>.</item>
<item>If Gt is a record field index <c>#Name.Field</c>,
where <c>Field</c> is an atom, then
Rep(Gt) = <c>{record_index,LINE,Name,Rep(Field)}</c>.</item>
<item>If Gt is a tuple skeleton <c>{Gt_1, ..., Gt_k}</c>, then
Rep(Gt) = <c>{tuple,LINE,[Rep(Gt_1), ..., Rep(Gt_k)]}</c>.</item>
<item>If Gt is a variable pattern <c>V</c>, then
Rep(Gt) = <c>{var,LINE,A}</c>, where A is an atom with
a printname consisting of the same characters as <c>V</c>.</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>Types</title>
<list type="bulleted">
<item>If T is an annotated type <c>A :: T_0</c>,
where <c>A</c> is a variable, then Rep(T) =
<c>{ann_type,LINE,[Rep(A),Rep(T_0)]}</c>.</item>
<item>If T is an atom or integer literal L, then Rep(T) = Rep(L).
</item>
<item>If T is a bit string type <c><<_:M,_:_*N>></c>,
where <c>M</c> and <c>N</c> are singleton integer types, then Rep(T) =
<c>{type,LINE,binary,[Rep(M),Rep(N)]}</c>.</item>
<item>If T is the empty list type <c>[]</c>, then Rep(T) =
<c>{type,Line,nil,[]}</c>.</item>
<item>If T is a fun type <c>fun()</c>, then Rep(T) =
<c>{type,LINE,'fun',[]}</c>.</item>
<item>If T is a fun type <c>fun((...) -> T_0)</c>, then
Rep(T) = <c>{type,LINE,'fun',[{type,LINE,any},Rep(T_0)]}</c>.
</item>
<item>If T is a fun type <c>fun(Ft)</c>, where
<c>Ft</c> is a function type,
then Rep(T) = <c>Rep(Ft)</c>. For Rep(Ft), see below.</item>
<item>If T is an integer range type <c>L .. H</c>,
where <c>L</c> and <c>H</c> are singleton integer types, then
Rep(T) = <c>{type,LINE,range,[Rep(L),Rep(H)]}</c>.</item>
<item>If T is a map type <c>map()</c>, then Rep(T) =
<c>{type,LINE,map,any}</c>.</item>
<item>If T is a map type <c>#{A_1, ..., A_k}</c>, where each
<c>A_i</c> is an association type, then Rep(T) =
<c>{type,LINE,map,[Rep(A_1), ..., Rep(A_k)]}</c>.
For Rep(A), see below.</item>
<item>If T is an operator type <c>T_1 Op T_2</c>,
where <c>Op</c> is a binary operator (this is an occurrence of
an expression that can be evaluated to an integer at compile
time), then
Rep(T) = <c>{op,LINE,Op,Rep(T_1),Rep(T_2)}</c>.</item>
<item>If T is an operator type <c>Op T_0</c>, where <c>Op</c> is a
unary operator (this is an occurrence of
an expression that can be evaluated to an integer at compile time),
then Rep(T) = <c>{op,LINE,Op,Rep(T_0)}</c>.</item>
<item>If T is <c>( T_0 )</c>, then Rep(T) = <c>Rep(T_0)</c>,
that is, parenthesized types cannot be distinguished from their
bodies.</item>
<item>If T is a predefined (or built-in) type <c>N(T_1, ..., T_k)</c>,
then Rep(T) =
<c>{type,LINE,N,[Rep(T_1), ..., Rep(T_k)]}</c>.</item>
<item>If T is a record type <c>#Name{F_1, ..., F_k}</c>,
where each <c>F_i</c> is a record field type, then Rep(T) =
<c>{type,LINE,record,[Rep(Name),Rep(F_1), ..., Rep(F_k)]}</c>.
For Rep(F), see below.</item>
<item>If T is a remote type <c>M:N(T_1, ..., T_k)</c>, then Rep(T) =
<c>{remote_type,LINE,[Rep(M),Rep(N),[Rep(T_1), ..., Rep(T_k)]]}</c>.
</item>
<item>If T is a tuple type <c>tuple()</c>, then Rep(T) =
<c>{type,LINE,tuple,any}</c>.</item>
<item>If T is a tuple type <c>{T_1, ..., T_k}</c>, then Rep(T) =
<c>{type,LINE,tuple,[Rep(T_1), ..., Rep(T_k)]}</c>.</item>
<item>If T is a type union <c>T_1 | ... | T_k</c>, then Rep(T) =
<c>{type,LINE,union,[Rep(T_1), ..., Rep(T_k)]}</c>.</item>
<item>If T is a type variable <c>V</c>, then Rep(T) =
<c>{var,LINE,A}</c>, where <c>A</c> is an atom with a printname
consisting of the same characters as <c>V</c>. A type variable
is any variable except underscore (<c>_</c>).</item>
<item>If T is a user-defined type <c>N(T_1, ..., T_k)</c>,
then Rep(T) =
<c>{user_type,LINE,N,[Rep(T_1), ..., Rep(T_k)]}</c>.</item>
</list>
<section>
<title>Function Types</title>
<p>A function type Ft is one of the following alternatives:</p>
<list type="bulleted">
<item>If Ft is a constrained function type <c>Ft_1 when Fc</c>,
where <c>Ft_1</c> is a function type and
<c>Fc</c> is a function constraint, then Rep(T) =
<c>{type,LINE,bounded_fun,[Rep(Ft_1),Rep(Fc)]}</c>.
For Rep(Fc), see below.</item>
<item>If Ft is a function type <c>(T_1, ..., T_n) -> T_0</c>,
where each <c>T_i</c> is a type, then
Rep(Ft) = <c>{type,LINE,'fun',[{type,LINE,product,[Rep(T_1),
..., Rep(T_n)]},Rep(T_0)]}</c>.</item>
</list>
</section>
<section>
<title>Function Constraints</title>
<p>A function constraint Fc is a nonempty sequence of constraints
<c>C_1, ..., C_k</c>, and
Rep(Fc) = <c>[Rep(C_1), ..., Rep(C_k)]</c>.</p>
<list type="bulleted">
<item>If C is a constraint <c>is_subtype(V, T)</c> or <c>V :: T</c>,
where <c>V</c> is a type variable and <c>T</c> is a type, then
Rep(C) = <c>{type,LINE,constraint,[{atom,LINE,is_subtype},[Rep(V),Rep(T)]]}</c>.
</item>
</list>
</section>
<section>
<title>Association Types</title>
<list type="bulleted">
<item>If A is an association type <c>K => V</c>, where
<c>K</c> and <c>V</c> are types, then Rep(A) =
<c>{type,LINE,map_field_assoc,[Rep(K),Rep(V)]}</c>.</item>
<item>If A is an association type <c>K := V</c>, where
<c>K</c> and <c>V</c> are types, then Rep(A) =
<c>{type,LINE,map_field_exact,[Rep(K),Rep(V)]}</c>.</item>
</list>
</section>
<section>
<title>Record Field Types</title>
<list type="bulleted">
<item>If F is a record field type <c>Name :: Type</c>,
where <c>Type</c> is a type, then Rep(F) =
<c>{type,LINE,field_type,[Rep(Name),Rep(Type)]}</c>.</item>
</list>
</section>
</section>
<section>
<title>The Abstract Format After Preprocessing</title>
<p>The compilation option <c>debug_info</c> can be given to the
compiler to have the abstract code stored in
the <c>abstract_code</c> chunk in the BEAM file
(for debugging purposes).</p>
<p>In OTP R9C and later, the <c>abstract_code</c> chunk will
contain</p>
<p><c>{raw_abstract_v1,AbstractCode}</c></p>
<p>where <c>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>abstract_v1</c> (R7B) or <c>abstract_v2</c>
(R8B).</p>
</section>
</chapter>
