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# epp

### MODULE

epp

### MODULE SUMMARY

An Erlang Code Preprocessor

### DESCRIPTION

The Erlang code preprocessor includes functions which are used by compile to preprocess macros and include files before the actual 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 that matches 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(), term()}]

epp_handle() = pid()

Handle to the epp server.

source_encoding() = latin1 | utf8

### EXPORTS

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

Types:

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

Opens a file for preprocessing.

close(Epp) -> ok

Types:

Epp = epp_handle()

Closes the preprocessing of a file.

parse_erl_form(Epp) ->
{ok, AbsForm} | {eof, Line} | {error, ErrorInfo}

Types:

Epp = epp_handle()
AbsForm = erl_parse:abstract_form()
Line = erl_scan:line()
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()

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

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, Line}
PredefMacros = macros()
Line = erl_scan:line()
ErrorInfo = erl_scan:error_info() | erl_parse:error_info()
OpenError = file:posix() | badarg | system_limit

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

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 as a valid encoding.

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 was found.

The 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 was found.

The 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.

set_encoding(File) -> source_encoding() | none

Types:

File = io:device()

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

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

format_error(ErrorDescriptor) -> io_lib:chars()

Types:

ErrorDescriptor = term()

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

### Error Information

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

        {ErrorLine, Module, ErrorDescriptor}

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

        Module:format_error(ErrorDescriptor)

### See Also

erl_parse(3)