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User's Guide
Version 1.7

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- Erlang Syntax and Metaprogramming tools
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  - Overview

# 1 Erlang Syntax and Metaprogramming tools

### 1.1 Overview

This package contains modules for handling abstract syntax trees (ASTs) in Erlang, in a way that is compatible with the "abstract format" parse trees of the stdlib module erl_parse, together with utilities for reading source files, pretty-printing syntax trees, merging and renaming modules, cleaning up obsolete constructs, and doing metaprogramming in Erlang.

The abstract layer (defined in erl_syntax) is nicely structured and the node types are context-independent. The layer makes it possible to transparently attach source-code comments and user annotations to nodes of the tree. Using the abstract layer makes applications less sensitive to changes in the erl_parse(3) data structures, only requiring the erl_syntax module to be up-to-date.

The pretty printer erl_prettypr is implemented on top of the library module prettypr: this is a powerful and flexible generic pretty printing library, which is also distributed separately.

For a short demonstration of parsing and pretty-printing, simply compile the included module demo.erl, and execute demo:run() from the Erlang shell. It will compile the remaining modules and give you further instructions.

Also try the erl_tidy module, as follows:

       erl_tidy:dir("any-erlang-source-dir", [test, old_guard_tests]).

(the test option assures that no files are modified).