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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() = {Tag :: atom(), Line :: erl_scan:line()}

### 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.

### 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