Erlang parse tools

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# Erlang parse tools

---
## Motivation
### Pretty print formatter

.left[![Screenshot](./pretty_print_screenshot.png)]

> Elixir library for coloring the output of the logger. Right now it colorizes Ecto SQL statements and Phoenix's request id metadata.
> The idea is to use colors as a way to help developers to spot easier in the console what's happening quickly.
>> https://github.com/san650/pretty_print_formatter

---
## Motivation
### Pretty print formatter

#### Input
```elixir
"SELECT * FROM users AS u0 WHERE u0.id = 5 LIMIT 10 OFFSET 50"
```

#### Output
```elixir
[
	{:keyword, 'SELECT'},
	{:operator, '*'},
	{:keyword, 'FROM'},
	{:name, 'users'},
	{:keyword, 'AS'},
	. . .
]
```

???
* Mention it's used to colorize the keywords
* Mention how hard it would be to code those rules by ourselves.

---
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## Erlang parse tools

---
### Leex
* Lexical analyzer generator for Erlang.

* Takes a string and returns a list of tokens.

* This rules are defined in a `.xrl` file.

* Takes that file as input and generates Erlang code.

---
```leex
Definitions.

INTEGER    = [0-9]+
FLOAT      = [0-9]+\.[0-9]+((E|e)(\+|\-)?[0-9]+)?
WHITESPACE = [\s\t\n\r]+

Rules.

{INTEGER} :
  {token, {number, TokenLine, TokenChars}}.

{FLOAT} :
  {token, {number, TokenLine, TokenChars}}.

\+ :
  {token, {'+', TokenLine}}.

{WHITESPACE} : skip_token.

Erlang code.

% Erlang code
```

--
#### Example
```elixir
"2 + 5.3" |> to_charlist |> :lexer.string
# [{:number, 1, "2"}, {:+, 1}, {:number, 1, "5.3"}]
```

???
* TokenLine: returns the line
* TokenChars: the matched string in the regex
* Show the an example with "select"
* Mention in creates an erlang module with the name of the file. Implements "string"

---
.left[![Screenshot](./tree.png)]

---
### Yecc
* Parser generator for Erlang (similar to `leex`).

* Takes a list of token and creates an structure (usually a tree) that we can process later.

* Takes a `.yrl` file with the grammar rules and generates Erlang code.

???
* Grammar defined using Backus-Naur form

---
```yrl
Nonterminals E.

Terminals '+' '*' '(' ')' number.

Rootsymbol E.

Left 100 '+'.
Left 200 '*'.

E -> E '+' E   : {'$2', '$1', '$3'}.
E -> E '*' E   : {'$2', '$1', '$3'}.
E -> '(' E ')' : '$2'.
E -> number    : '$1'.

Erlang code.

% Erlang code
```

--
#### Example
```elixir
"2 * 5 + 3" |> to_charlist |> :lexer.string |> :grammar.parse
#{{:+, 1},
#  {{:*, 1},
#    {:number, 1, "2"},
#    {:number, 1, "5"}
#  },
#  {:number, 1, "3"}
#}
```

???
Mention an example with other nonterminal element

---
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# Let's see some code in action!

---
class: credits
# Thanks!
  
### Ignacio Aguirrezabal
* **GitHub**:  https://github.com/iaguirre88
* **Twitter**: https://twitter.com/iaguirre88

#### References
* **pretty_print_formatter**: https://github.com/san650/pretty_print_formatter

* **Tokenizing and parsing in Elixir with yecc and leex**: https://andrealeopardi.com/posts/tokenizing-and-parsing-in-elixir-using-leex-and-yecc/

* **Erlang Parse Tools Reference Manual**: http://erlang.org/doc/apps/parsetools/index.html