epp (stdlib v7.0)

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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 -*-

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)

See Also

erl_parse

Summary

Types

epp_handle()

Handle to the epp server.

macros()
source_encoding()
warning_info()

Functions

close(Epp)

Closes the preprocessing of a file.

default_encoding()

Returns the default encoding of Erlang source files.

encoding_to_string(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)

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)

Opens a file for preprocessing.

open(FileName, IncludePath)

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

open(FileName, IncludePath, PredefMacros)

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

parse_erl_form(Epp)

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)

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

parse_file(FileName, IncludePath, PredefMacros)

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

read_encoding(FileName)

Equivalent to read_encoding/2.

read_encoding(FileName, Options)

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

read_encoding_from_binary(Binary)

Equivalent to read_encoding_from_binary/2.

read_encoding_from_binary(Binary, Options)

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

scan_erl_form(Epp)

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)

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)

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.

set_encoding(File, Default)

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.

Types

epp_handle()

(not exported) 
-type epp_handle() :: pid().

Handle to the epp server.

macros()

(not exported) 
-type macros() :: [atom() | {atom(), term()} | {atom(), term(), redefine}].

source_encoding()

-type source_encoding() :: latin1 | utf8.

warning_info()

(not exported) 
-type warning_info() :: {erl_anno:location(), module(), term()}.

Functions

close(Epp)

-spec close(Epp) -> ok when Epp :: epp_handle().

Closes the preprocessing of a file.

default_encoding()

(since OTP R16B) 
-spec default_encoding() -> source_encoding().

Returns the default encoding of Erlang source files.

encoding_to_string(Encoding)

(since OTP R16B) 
-spec encoding_to_string(Encoding) -> string() when 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)

(since OTP R14B03) 
-spec format_error(ErrorDescriptor) -> io_lib:chars() when 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)

(since OTP 17.0) 
-spec open(Options) -> {ok, Epp} | {ok, Epp, Extra} | {error, ErrorDescriptor}
              when
                  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 |
                       {compiler_internal, [term()]}],
                  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.

The {compiler_internal,term()} option is forwarded to the Erlang token scanner, see {compiler_internal,term()}.

open(FileName, IncludePath)

-spec open(FileName, IncludePath) -> {ok, Epp} | {error, ErrorDescriptor}
              when
                  FileName :: file:name(),
                  IncludePath :: [DirectoryName :: file:name()],
                  Epp :: epp_handle(),
                  ErrorDescriptor :: term().

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

open(FileName, IncludePath, PredefMacros)

-spec open(FileName, IncludePath, PredefMacros) -> {ok, Epp} | {error, ErrorDescriptor}
              when
                  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)

-spec parse_erl_form(Epp) ->
                        {ok, AbsForm} | {error, ErrorInfo} | {warning, WarningInfo} | {eof, Location}
                        when
                            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)

(since OTP 17.0) 
-spec parse_file(FileName, Options) -> {ok, [Form]} | {ok, [Form], Extra} | {error, OpenError}
                    when
                        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 |
                             {compiler_internal, [term()]}],
                        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.

The {compiler_internal,term()} option is forwarded to the Erlang token scanner, see {compiler_internal,term()}.

parse_file(FileName, IncludePath, PredefMacros)

-spec parse_file(FileName, IncludePath, PredefMacros) -> {ok, [Form]} | {error, OpenError}
                    when
                        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)

(since OTP R16B) 
-spec read_encoding(FileName) -> source_encoding() | none when FileName :: file:name().

Equivalent to read_encoding/2.

read_encoding(FileName, Options)

(since OTP R16B) 
-spec read_encoding(FileName, Options) -> source_encoding() | none
                       when
                           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)

(since OTP R16B) 
-spec read_encoding_from_binary(Binary) -> source_encoding() | none when Binary :: binary().

Equivalent to read_encoding_from_binary/2.

read_encoding_from_binary(Binary, Options)

(since OTP R16B) 
-spec read_encoding_from_binary(Binary, Options) -> source_encoding() | none
                                   when
                                       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)

(since OTP R13B03) 
-spec scan_erl_form(Epp) -> {ok, Tokens} | {error, ErrorInfo} | {warning, WarningInfo} | {eof, Line}
                       when
                           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)

(since OTP 24.0) 
-spec scan_file(FileName, Options) -> {ok, [Form], Extra} | {error, OpenError}
                   when
                       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)

(since OTP R16B) 
-spec set_encoding(File) -> source_encoding() | none when 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)

(since OTP 17.0) 
-spec set_encoding(File, Default) -> source_encoding() | none
                      when 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.