# epp

###
Module

epp

###
Module Summary

An Erlang code preprocessor.

###
Description

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 -*-

###
Data Types

####
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()}

###
Exports

####
close(Epp) -> ok

### Types

Epp = epp_handle()

Closes the preprocessing of a file.

####
default_encoding() -> source_encoding()
OTP R16B

Returns the default encoding of Erlang source files.

####
encoding_to_string(Encoding) -> string()
OTP R16B

### 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()
OTP R14B03

### 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}
OTP 17.0

### Types

Options =
[{default_encoding, DefEncoding :: source_encoding()} |
{includes, IncludePath :: [DirectoryName :: file:name()]} |
{source_name, SourceName :: file:name()} |
{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.

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}
OTP 17.0

### 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()} |
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
OTP R16B

####
read_encoding(FileName, Options) -> source_encoding() | none
OTP R16B

### 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
OTP R16B

####
read_encoding_from_binary(Binary, Options) ->
source_encoding() | none
OTP R16B

### 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}
OTP R13B03

### 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}
OTP 24.0

### 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
OTP R16B

### 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
OTP 17.0

### 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.

###
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(3)