DOKK / manpages / debian 12 / erlang-manpages / epp.3erl.en
epp(3erl) Erlang Module Definition epp(3erl)

epp - An Erlang code preprocessor.

The Erlang code preprocessor includes functions that are used by the compile module to preprocess macros and include files before the parsing takes place.

The Erlang source file encoding is selected by a comment in one of the first two lines of the source file. The first string matching the regular expression coding\s*[:=]\s*([-a-zA-Z0-9])+ selects the encoding. If the matching string is not a valid encoding, it is ignored. The valid encodings are Latin-1 and UTF-8, where the case of the characters can be chosen freely.

Examples:

%% coding: utf-8

%% For this file we have chosen encoding = Latin-1

%% -*- coding: latin-1 -*-

macros() = 


    [atom() | {atom(), term()} | {atom(), term(), redefine}]



epp_handle() = pid()

Handle to the epp server.

source_encoding() = latin1 | utf8



warning_info() = {erl_anno:location(), module(), term()}





close(Epp) -> ok

Types:

Epp = epp_handle()

Closes the preprocessing of a file.


default_encoding() -> source_encoding()

Returns the default encoding of Erlang source files.


encoding_to_string(Encoding) -> string()

Types:

Encoding = source_encoding()

Returns a string representation of an encoding. The string is recognized by read_encoding/1,2, read_encoding_from_binary/1,2, and set_encoding/1,2 as a valid encoding.


format_error(ErrorDescriptor) -> io_lib:chars()

Types:

ErrorDescriptor = term()

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


open(Options) ->



        {ok, Epp} | {ok, Epp, Extra} | {error, ErrorDescriptor}

Types:

Options =
[{default_encoding, DefEncoding :: source_encoding()} |
{includes, IncludePath :: [DirectoryName :: file:name()]} |
{source_name, SourceName :: file:name()} |
{deterministic, Enabled :: boolean()} |
{macros, PredefMacros :: macros()} |
{name, FileName :: file:name()} |
{location, StartLocation :: erl_anno:location()} |
{fd, FileDescriptor :: file:io_device()} |
extra]
Epp = epp_handle()
Extra = [{encoding, source_encoding() | none}]
ErrorDescriptor = term()

Opens a file for preprocessing.

If you want to change the file name of the implicit -file() attributes inserted during preprocessing, you can do with {source_name, SourceName}. If unset it will default to the name of the opened file.

Setting {deterministic, Enabled} will additionally reduce the file name of the implicit -file() attributes inserted during preprocessing to only the basename of the path.

If extra is specified in Options, the return value is {ok, Epp, Extra} instead of {ok, Epp}.

The option location is forwarded to the Erlang token scanner, see erl_scan:tokens/3,4.


open(FileName, IncludePath) ->



        {ok, Epp} | {error, ErrorDescriptor}

Types:

FileName = file:name()
IncludePath = [DirectoryName :: file:name()]
Epp = epp_handle()
ErrorDescriptor = term()

Equivalent to epp:open([{name, FileName}, {includes, IncludePath}]).


open(FileName, IncludePath, PredefMacros) ->



        {ok, Epp} | {error, ErrorDescriptor}

Types:

FileName = file:name()
IncludePath = [DirectoryName :: file:name()]
PredefMacros = macros()
Epp = epp_handle()
ErrorDescriptor = term()

Equivalent to epp:open([{name, FileName}, {includes, IncludePath}, {macros, PredefMacros}]).


parse_erl_form(Epp) ->



                  {ok, AbsForm} |



                  {error, ErrorInfo} |



                  {warning, WarningInfo} |



                  {eof, Location}

Types:

Epp = epp_handle()
AbsForm = erl_parse:abstract_form()
Location = erl_anno:location()
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()
WarningInfo = warning_info()

Returns the next Erlang form from the opened Erlang source file. Tuple {eof, Location} is returned at the end of the file. The first form corresponds to an implicit attribute -file(File,1)., where File is the file name.


parse_file(FileName, Options) ->



              {ok, [Form]} |



              {ok, [Form], Extra} |



              {error, OpenError}

Types:

FileName = file:name()
Options =
[{includes, IncludePath :: [DirectoryName :: file:name()]} |
{source_name, SourceName :: file:name()} |
{macros, PredefMacros :: macros()} |
{default_encoding, DefEncoding :: source_encoding()} |
{location, StartLocation :: erl_anno:location()} |
{reserved_word_fun, Fun :: fun((atom()) -> boolean())} |
{features, [Feature :: atom()]} |
extra]
Form =
erl_parse:abstract_form() |
{error, ErrorInfo} |
{eof, Location}
Location = erl_anno:location()
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()
Extra = [{encoding, source_encoding() | none}]
OpenError = file:posix() | badarg | system_limit

Preprocesses and parses an Erlang source file. Notice that tuple {eof, Location} returned at the end of the file is included as a "form".

If you want to change the file name of the implicit -file() attributes inserted during preprocessing, you can do with {source_name, SourceName}. If unset it will default to the name of the opened file.

If extra is specified in Options, the return value is {ok, [Form], Extra} instead of {ok, [Form]}.

The option location is forwarded to the Erlang token scanner, see erl_scan:tokens/3,4.


parse_file(FileName, IncludePath, PredefMacros) ->



              {ok, [Form]} | {error, OpenError}

Types:

FileName = file:name()
IncludePath = [DirectoryName :: file:name()]
Form =
erl_parse:abstract_form() |
{error, ErrorInfo} |
{eof, Location}
PredefMacros = macros()
Location = erl_anno:location()
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()
OpenError = file:posix() | badarg | system_limit

Equivalent to epp:parse_file(FileName, [{includes, IncludePath}, {macros, PredefMacros}]).


read_encoding(FileName) -> source_encoding() | none





read_encoding(FileName, Options) -> source_encoding() | none

Types:

FileName = file:name()
Options = [Option]
Option = {in_comment_only, boolean()}

Read the encoding from a file. Returns the read encoding, or none if no valid encoding is found.

Option in_comment_only is true by default, which is correct for Erlang source files. If set to false, the encoding string does not necessarily have to occur in a comment.


read_encoding_from_binary(Binary) -> source_encoding() | none





read_encoding_from_binary(Binary, Options) ->



                             source_encoding() | none

Types:

Binary = binary()
Options = [Option]
Option = {in_comment_only, boolean()}

Read the encoding from a binary. Returns the read encoding, or none if no valid encoding is found.

Option in_comment_only is true by default, which is correct for Erlang source files. If set to false, the encoding string does not necessarily have to occur in a comment.


scan_erl_form(Epp) ->



                 {ok, Tokens} |



                 {error, ErrorInfo} |



                 {warning, WarningInfo} |



                 {eof, Line}

Types:

Epp = epp_handle()
Tokens = erl_scan:tokens()
Line = erl_anno:line()
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()
WarningInfo = warning_info()

Returns the raw tokens of the next Erlang form from the opened Erlang source file. A tuple {eof, Line} is returned at the end of the file. The first form corresponds to an implicit attribute -file(File,1)., where File is the file name.


scan_file(FileName, Options) ->



             {ok, [Form], Extra} | {error, OpenError}

Types:

FileName = file:name()
Options =
[{includes, IncludePath :: [DirectoryName :: file:name()]} |
{source_name, SourceName :: file:name()} |
{macros, PredefMacros :: macros()} |
{default_encoding, DefEncoding :: source_encoding()}]
Form = erl_scan:tokens() | {error, ErrorInfo} | {eof, Loc}
Loc = erl_anno:location()
ErrorInfo = erl_scan:error_info()
Extra = [{encoding, source_encoding() | none}]
OpenError = file:posix() | badarg | system_limit

Preprocesses an Erlang source file returning a list of the lists of raw tokens of each form. Notice that the tuple {eof, Line} returned at the end of the file is included as a "form", and any failures to scan a form are included in the list as tuples {error, ErrorInfo}.


set_encoding(File) -> source_encoding() | none

Types:

File = io:device()

Reads the encoding from an I/O device and sets the encoding of the device accordingly. The position of the I/O device referenced by File is not affected. If no valid encoding can be read from the I/O device, the encoding of the I/O device is set to the default encoding.

Returns the read encoding, or none if no valid encoding is found.


set_encoding(File, Default) -> source_encoding() | none

Types:

Default = source_encoding()
File = io:device()

Reads the encoding from an I/O device and sets the encoding of the device accordingly. The position of the I/O device referenced by File is not affected. If no valid encoding can be read from the I/O device, the encoding of the I/O device is set to the encoding specified by Default.

Returns the read encoding, or none if no valid encoding is found.

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)

erl_parse(3erl)

stdlib 4.2 Ericsson AB