# 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).

### EXPORTS

parse_form(Tokens) -> {ok, AbsForm} | {error, ErrorInfo}

Types:

Tokens = [Token]
Token = {Tag,Line} | {Tag,Line,term()}
Tag = atom()
AbsForm = term()
ErrorInfo = see section Error Information below.

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, Expr_list} | {error, ErrorInfo}

Types:

Tokens = [Token]
Token = {Tag,Line} | {Tag,Line,term()}
Tag = atom()
Expr_list = [AbsExpr]
AbsExpr = term()
ErrorInfo = see section Error Information below.

This function parses Tokens as if it were a list of expressions. It returns:

{ok, Expr_list}
  The parsing was successful. Expr_list 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]
Token = {Tag,Line} | {Tag,Line,term()}
Tag = atom()
Term = term()
ErrorInfo = see section Error Information below.

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 = errordesc()
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:

Tokens = MoreTokens = [Token]
Token = {Tag,Line} | {Tag,Line,term()}
Tag = atom()
AbsTerm = term()
ErrorInfo = see section Error Information below.

This function generates a list of tokens representing the abstract form AbsTerm of an expression. Optionally, it appends Moretokens.

normalise(AbsTerm) -> Data

Types:

AbsTerm = 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 = AbsTerm = term()

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:

    apply(Module, format_error, ErrorDescriptor)

### See Also

io(3), erl_scan(3), ERTS User's Guide

stdlib 1.15.4
Copyright © 1991-2008 Ericsson AB