# erl_parse

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Module

erl_parse

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Module Summary

The Erlang parser.

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Description

This module is the basic Erlang parser that converts tokens into the abstract form of either forms (that is, top-level constructs), expressions, or terms. The Abstract Format is described in the ERTS User's Guide. Notice that a token list must end with the dot token to be acceptable to the parse functions (see the erl_scan(3)) module.

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Data Types

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abstract_clause()

Abstract form of an Erlang clause.

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abstract_expr()

Abstract form of an Erlang expression.

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abstract_form()

Abstract form of an Erlang form.

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abstract_type()

Abstract form of an Erlang type.

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erl_parse_tree() =
abstract_clause() |
abstract_expr() |
abstract_form() |
abstract_type()

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af_binelement(_)

Abstract representation of an element of a bitstring.

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af_field_decl()

Abstract representation of a record field.

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af_generator()

Abstract representation of a generator or a bitstring generator.

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af_remote_function()>

Abstract representation of a remote function call.

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error_description() = term()

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error_info() =
{erl_anno:location(), module(), error_description()}

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form_info() =
{eof, erl_anno:location()} |
{error, erl_scan:error_info() | error_info()} |
{warning, erl_scan:error_info() | error_info()}

Tuples {error, error_info()} and {warning, error_info()}, denoting syntactically incorrect forms and warnings, and {eof, line()}, denoting an end-of-stream encountered before a complete form had been parsed.

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token() = erl_scan:token()

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Exports

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abstract(Data) -> AbsTerm

### Types

Data = term()
AbsTerm = abstract_expr()

Converts the Erlang data structure Data into an abstract form of type AbsTerm. This function is the inverse of normalise/1.

erl_parse:abstract(T) is equivalent to erl_parse:abstract(T, 0).

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abstract(Data, Options) -> AbsTerm
OTP R16B01

### Types

Data = term()
Options = Location | [Option]
Option =
{encoding, Encoding} | {line, Line} | {location, Location}
Encoding = latin1 | unicode | utf8 | none | encoding_func()
Line = erl_anno:line()
Location = erl_anno:location()
AbsTerm = abstract_expr()
encoding_func() = fun((integer() >= 0) -> boolean())

Converts the Erlang data structure Data into an abstract form of type AbsTerm.

Each node of AbsTerm is assigned an annotation, see erl_anno(3). The annotation contains the location given by option location or by option line. Option location overrides option line. If neither option location nor option line is given, 0 is used as location.

Option Encoding is used for selecting which integer lists to be considered as strings. The default is to use the encoding returned by function epp:default_encoding/0. Value none means that no integer lists are considered as strings. encoding_func() is called with one integer of a list at a time; if it returns true for every integer, the list is considered a string.

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anno_from_term(Term) -> erl_parse_tree() | form_info()
OTP 18.0

### Types

Term = term()

Assumes that Term is a term with the same structure as a erl_parse tree, but with terms, say T, where a erl_parse tree has collections of annotations. Returns a erl_parse tree where each term T is replaced by the value returned by erl_anno:from_term(T). The term Term is traversed in a depth-first, left-to-right fashion.

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anno_to_term(Abstr) -> term()
OTP 18.0

### Types

Abstr = erl_parse_tree() | form_info()

Returns a term where each collection of annotations Anno of the nodes of the erl_parse tree Abstr is replaced by the term returned by erl_anno:to_term(Anno). The erl_parse tree is traversed in a depth-first, left-to-right fashion.

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fold_anno(Fun, Acc0, Abstr) -> Acc1
OTP 18.0

### Types

Fun = fun((Anno, AccIn) -> AccOut)
Anno = erl_anno:anno()
Acc0 = Acc1 = AccIn = AccOut = term()
Abstr = erl_parse_tree() | form_info()

Updates an accumulator by applying Fun on each collection of annotations of the erl_parse tree Abstr. The first call to Fun has AccIn as argument, the returned accumulator AccOut is passed to the next call, and so on. The final value of the accumulator is returned. The erl_parse tree is traversed in a depth-first, left-to-right fashion.

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format_error(ErrorDescriptor) -> Chars

### Types

ErrorDescriptor = error_description()
Chars = [char() | Chars]

Uses an ErrorDescriptor and returns a string that describes the error. This function is usually called implicitly when an ErrorInfo structure is processed (see section Error Information).

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map_anno(Fun, Abstr) -> NewAbstr
OTP 18.0

### Types

Fun = fun((Anno) -> NewAnno)
Anno = NewAnno = erl_anno:anno()
Abstr = NewAbstr = erl_parse_tree() | form_info()

Modifies the erl_parse tree Abstr by applying Fun on each collection of annotations of the nodes of the erl_parse tree. The erl_parse tree is traversed in a depth-first, left-to-right fashion.

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mapfold_anno(Fun, Acc0, Abstr) -> {NewAbstr, Acc1}
OTP 18.0

### Types

Fun = fun((Anno, AccIn) -> {NewAnno, AccOut})
Anno = NewAnno = erl_anno:anno()
Acc0 = Acc1 = AccIn = AccOut = term()
Abstr = NewAbstr = erl_parse_tree() | form_info()

Modifies the erl_parse tree Abstr by applying Fun on each collection of annotations of the nodes of the erl_parse tree, while at the same time updating an accumulator. The first call to Fun has AccIn as second argument, the returned accumulator AccOut is passed to the next call, and so on. The modified erl_parse tree and the final value of the accumulator are returned. The erl_parse tree is traversed in a depth-first, left-to-right fashion.

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new_anno(Term) -> Abstr
OTP 18.0

### Types

Term = term()
Abstr = erl_parse_tree() | form_info()

Assumes that Term is a term with the same structure as a erl_parse tree, but with locations where a erl_parse tree has collections of annotations. Returns a erl_parse tree where each location L is replaced by the value returned by erl_anno:new(L). The term Term is traversed in a depth-first, left-to-right fashion.

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normalise(AbsTerm) -> Data

### Types

AbsTerm = abstract_expr()
Data = term()

Converts the abstract form AbsTerm of a term into a conventional Erlang data structure (that is, the term itself). This function is the inverse of abstract/1.

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parse_exprs(Tokens) -> {ok, ExprList} | {error, ErrorInfo}

### Types

Tokens = [token()]
ExprList = [abstract_expr()]
ErrorInfo = error_info()

Parses Tokens as if it was a list of expressions. Returns one of the following:

{ok, ExprList}

  The parsing was successful. ExprList is a list of the abstract forms of the parsed expressions.

{error, ErrorInfo}

  An error occurred.

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parse_form(Tokens) -> {ok, AbsForm} | {error, ErrorInfo}

### Types

Tokens = [token()]
AbsForm = abstract_form()
ErrorInfo = error_info()

Parses Tokens as if it was a form. Returns one of the following:

{ok, AbsForm}

  The parsing was successful. AbsForm is the abstract form of the parsed form.

{error, ErrorInfo}

  An error occurred.

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parse_term(Tokens) -> {ok, Term} | {error, ErrorInfo}

### Types

Tokens = [token()]
Term = term()
ErrorInfo = error_info()

Parses Tokens as if it was a term. Returns one of the following:

{ok, Term}

  The parsing was successful. Term is the Erlang term corresponding to the token list.

{error, ErrorInfo}

  An error occurred.

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tokens(AbsTerm) -> Tokens

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tokens(AbsTerm, MoreTokens) -> Tokens

### Types

AbsTerm = abstract_expr()
MoreTokens = Tokens = [token()]

Generates a list of tokens representing the abstract form AbsTerm of an expression. Optionally, MoreTokens is appended.

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Error Information

ErrorInfo is the standard ErrorInfo structure that is returned from all I/O modules. The format is as follows:

    {ErrorLine, Module, ErrorDescriptor}

A string describing the error is obtained with the following call:

    Module:format_error(ErrorDescriptor)

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See Also

erl_anno(3), erl_scan(3), io(3), section The Abstract Format in the ERTS User's Guide