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# erl_parse

### MODULE

erl_parse

### MODULE SUMMARY

The Erlang Parser

### DESCRIPTION

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

### DATA TYPES

abstract_clause() = term()

Parse tree for Erlang clause.

abstract_expr() = term()

Parse tree for Erlang expression.

abstract_form() = term()

Parse tree for Erlang form.

error_description() = term()

error_info() = {erl_scan:line(), module(), error_description()}

token() = erl_scan:token()

### EXPORTS

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

Types:

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

This function parses Tokens as if it were a form. It returns:

{ok, AbsForm}

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

{error, ErrorInfo}

  An error occurred.

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

Types:

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

This function parses Tokens as if it were a list of expressions. It returns:

{ok, ExprList}

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

{error, ErrorInfo}

  An error occurred.

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

Types:

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

This function parses Tokens as if it were a term. It returns:

{ok, Term}

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

{error, ErrorInfo}

  An error occurred.

format_error(ErrorDescriptor) -> Chars

Types:

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

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

tokens(AbsTerm) -> Tokens
tokens(AbsTerm, MoreTokens) -> Tokens

Types:

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

This function generates a list of tokens representing the abstract form AbsTerm of an expression. Optionally, it appends MoreTokens.

normalise(AbsTerm) -> Data

Types:

AbsTerm = abstract_expr()
Data = term()

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

abstract(Data) -> AbsTerm

Types:

Data = term()
AbsTerm = abstract_expr()

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

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

abstract(Data, Options) -> AbsTerm

Types:

Data = term()
Options = Line | [Option]
Option = {line, Line} | {encoding, Encoding}
Encoding = latin1 | unicode | utf8
Line = erl_scan:line()
AbsTerm = abstract_expr()

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

The Line option is the line that will be assigned to each node of the abstract form.

The Encoding option is used for selecting which integer lists will be considered as strings. The default is to use the encoding returned by epp:default_encoding/0

### Error Information

The ErrorInfo mentioned above is the standard ErrorInfo structure which is returned from all IO modules. It has the format:

        {ErrorLine, Module, ErrorDescriptor}

A string which describes the error is obtained with the following call:

        Module:format_error(ErrorDescriptor)

### See Also

io(3), erl_scan(3), ERTS User's Guide