pyleri 1.2.0

Python Left-Right Parser

Python Left-Right Parser
========================
Pyleri is an easy-to-use parser created for [SiriDB](http://siridb.net/). We first used [lrparsing](http://lrparsing.sourceforge.net/doc/html/) and wrote [jsleri](https://github.com/transceptor-technology/jsleri) for auto-completion and suggestions in our web console. Later we found small issues within the `lrparsing` module and also had difficulties keeping the language the same in all projects. That is when we decided to create Pyleri which can export a created grammar to JavaScript, C, Python, Go and Java.

---------------------------------------
* [Related projects](#related-projects)
* [Installation](#installation)
* [Quick usage](#quick-usage)
* [Grammar](#grammar)
* [Grammar.parse()](#parse)
* [Grammar.export_js()](#export_js)
* [Grammar.export_c()](#export_c)
* [Grammar.export_go()](#export_go)
* [Grammar.export_java()](#export_java)
* [Grammar.export_py()](#export_py)
* [Elements](#elements)
* [Keyword](#keyword)
* [Regex](#regex)
* [Token](#token)
* [Tokens](#tokens)
* [Sequence](#sequence)
* [Choice](#choice)
* [Repeat](#repeat)
* [List](#list)
* [Optional](#optional)
* [Ref](#ref)
* [Prio](#prio)


---------------------------------------
## Related projects
- [jsleri](https://github.com/transceptor-technology/jsleri): JavaScript parser
- [libcleri](https://github.com/transceptor-technology/libcleri): C parser
- [goleri](https://github.com/transceptor-technology/goleri): Go parser
- [jleri](https://github.com/transceptor-technology/jleri): Java parser

## Installation
The easiest way is to use PyPI:

sudo pip3 install pyleri

## Quick usage
```python
# Imports, note that we skip the imports in other examples...
from pyleri import (
Grammar,
Keyword,
Regex,
Sequence)

# Create a Grammar Class to define your language
class MyGrammar(Grammar):
r_name = Regex('(?:"(?:[^"]*)")+')
k_hi = Keyword('hi')
START = Sequence(k_hi, r_name)

# Compile your grammar by creating an instance of the Grammar Class.
my_grammar = MyGrammar()

# Use the compiled grammar to parse 'strings'
print(my_grammar.parse('hi "Iris"').is_valid) # => True
print(my_grammar.parse('bye "Iris"').is_valid) # => False
```

## Grammar
When writing a grammar you should subclass Grammar. A Grammar expects at least a `START` property so the parser knows where to start parsing. Grammar has some default properties which can be overwritten like `RE_KEYWORDS` and `RE_WHITESPACE`, which are both explained later. Grammer also has a parse method: `parse()`, and a few export methods: `export_js()`, `export_c()`, `export_py()` and `export_go()` which are explained below.

### parse
syntax:
```python
Grammar().parse(string)
```
The `parse()` method returns a `NodeResult` object which has the following properties:
- `expecting`: A Python set() containing elements which pyleri expects at `pos`. Even if `is_valid` is true there might be elements in this set, for example when an `Optional()` element could be added to the string. Expecting is useful if you want to implement things like auto-completion, syntax error handling, auto-syntax-correction etc.
- `is_valid`: Boolean value, `True` when the given string is valid, `False` when not valid.
- `pos`: Position where the parser had to stop. (when `is_valid` is `True` this value will be equal to the length of the given string with `str.rstrip()` applied)
- `tree`: Contains the parse tree. Even when `is_valid` is `False` the parse tree is returned but will only contain results as far as parsing has succeeded.

Let us take the example from Quick usage.
```python
node_result = my_grammer.parse('bye "Iris"')
print(node_result.is_valid) # => False
print(node_result.expecting) # => {hi} => We expected Keyword 'hi' instead of bye
print(node_result.pos) # => 0 => Position in the string where we are expecting the above
print(node_result.tree) # => Node object containing the parse tree
```

### export_js
syntax:
```python
Grammar().export_js(
js_module_name='jsleri',
js_template=Grammar.JS_TEMPLATE,
js_indent=' ' * 4)
```
Optional keyword arguments:
- `js_module_name`: Name of the JavaScript module. (default: 'jsleri')
- `js_template`: Template String used for the export. You might want to look at the default string which can be found at Grammar.JS_TEMPLATE.
- `js_indent`: indentation used in the JavaScript file. (default: 4 spaces)

For example when using our Quick usage grammar, this is the output when running `my_grammar.export_js()`:
```javascript
/* jshint newcap: false */

/*
* This grammar is generated using the Grammar.export_js() method and
* should be used with the jsleri JavaScript module.
*
* Source class: MyGrammar
* Created at: 2015-11-04 10:06:06
*/

'use strict';

(function (
Regex,
Sequence,
Keyword,
Grammar
) {
var r_name = Regex('^(?:"(?:[^"]*)")+');
var k_hi = Keyword('hi');
var START = Sequence(
k_hi,
r_name
);

window.MyGrammar = Grammar(START, '^\w+');

})(
window.jsleri.Regex,
window.jsleri.Sequence,
window.jsleri.Keyword,
window.jsleri.Grammar
);
```

### export_c
syntax:
```python
Grammar().export_c(
target=Grammar.C_TARGET,
c_indent=' ' * 4)
```
Optional keyword arguments:
- `target`: Name of the c module. (default: 'grammar')
- `c_indent`: indentation used in the c files. (default: 4 spaces)

The return value is a tuple containing the source (c) file and header (h) file.

For example when using our Quick usage grammar, this is the output when running `my_grammar.export_c()`:
```c
/*
* grammar.c
*
* This grammar is generated using the Grammar.export_c() method and
* should be used with the libcleri module.
*
* Source class: MyGrammar
* Created at: 2016-05-09 12:16:49
*/

#include "grammar.h"
#include <stdio.h>

#define CLERI_CASE_SENSITIVE 0
#define CLERI_CASE_INSENSITIVE 1

#define CLERI_FIRST_MATCH 0
#define CLERI_MOST_GREEDY 1

cleri_grammar_t * compile_grammar(void)
{
cleri_t * r_name = cleri_regex(CLERI_GID_R_NAME, "^(?:\"(?:[^\"]*)\")+");
cleri_t * k_hi = cleri_keyword(CLERI_GID_K_HI, "hi", CLERI_CASE_INSENSITIVE);
cleri_t * START = cleri_sequence(
CLERI_GID_START,
2,
k_hi,
r_name
);

cleri_grammar_t * grammar = cleri_grammar(START, "^\\w+");

return grammar;
}
```
and the header file...
```c
/*
* grammar.h
*
* This grammar is generated using the Grammar.export_c() method and
* should be used with the libcleri module.
*
* Source class: MyGrammar
* Created at: 2016-05-09 12:16:49
*/
#ifndef CLERI_EXPORT_GRAMMAR_H_
#define CLERI_EXPORT_GRAMMAR_H_

#include <grammar.h>
#include <cleri/cleri.h>

cleri_grammar_t * compile_grammar(void);

enum cleri_grammar_ids {
CLERI_NONE, // used for objects with no name
CLERI_GID_K_HI,
CLERI_GID_R_NAME,
CLERI_GID_START,
CLERI_END // can be used to get the enum length
};

#endif /* CLERI_EXPORT_GRAMMAR_H_ */

```
### export_go
syntax:
```python
Grammar().export_go(
go_template=Grammar.GO_TEMPLATE,
go_indent='\t',
go_package='grammar')
```
Optional keyword arguments:
- `go_template`: Template String used for the export. You might want to look at the default string which can be found at Grammar.GO_TEMPLATE.
- `go_indent`: indentation used in the Go file. (default: one tab)
- `go_package`: Name of the go package. (default: 'grammar')

For example when using our Quick usage grammar, this is the output when running `my_grammar.export_go()`:
```go
package grammar

// This grammar is generated using the Grammar.export_go() method and
// should be used with the goleri module.
//
// Source class: MyGrammar
// Created at: 2017-03-14 19:07:09

import (
"regexp"

"github.com/transceptor-technology/goleri"
)

// Element indentifiers
const (
NoGid = iota
GidKHi = iota
GidRName = iota
GidSTART = iota
)

// MyGrammar returns a compiled goleri grammar.
func MyGrammar() *goleri.Grammar {
rName := goleri.NewRegex(GidRName, regexp.MustCompile(`^(?:"(?:[^"]*)")+`))
kHi := goleri.NewKeyword(GidKHi, "hi", false)
START := goleri.NewSequence(
GidSTART,
kHi,
rName,
)
return goleri.NewGrammar(START, regexp.MustCompile(`^\w+`))
}
```
### export_java
syntax:
```python
Grammar().export_java(
java_template=Grammar.JAVA_TEMPLATE,
java_indent=' ' * 4,
java_package=None,
is_public=True)
```
Optional keyword arguments:
- `java_template`: Template String used for the export. You might want to look at the default string which can be found at Grammar.JAVA_TEMPLATE.
- `java_indent`: indentation used in the Java file. (default: four spaces)
- `java_package`: Name of the Java package or None when no package is specified. (default: None)
- `is_public`: Class and constructor are defined as public when True, else they will be defined as package private.

For example when using our Quick usage grammar, this is the output when running `my_grammar.export_java()`:
```java
/**
* This grammar is generated using the Grammar.export_java() method and
* should be used with the jleri module.
*
* Source class: MyGrammar
* Created at: 2018-07-04 12:12:34
*/

import jleri.Grammar;
import jleri.Element;
import jleri.Sequence;
import jleri.Regex;
import jleri.Keyword;

public class MyGrammar extends Grammar {
enum Ids {
K_HI,
R_NAME,
START
}

private static final Element R_NAME = new Regex(Ids.R_NAME, "^(?:\"(?:[^\"]*)\")+");
private static final Element K_HI = new Keyword(Ids.K_HI, "hi", false);
private static final Element START = new Sequence(
Ids.START,
K_HI,
R_NAME
);

public MyGrammar() {
super(START, "^\\w+");
}
}
```
### export_py
syntax:
```python
Grammar().export_py(
py_module_name='pyleri',
py_template=Grammar.PY_TEMPLATE,
py_indent=' ' * 4)
```
Optional keyword arguments:
- `py_module_name`: Name of the Pyleri Module. (default: 'pyleri')
- `py_template`: Template String used for the export. You might want to look at the default string which can be found at Grammar.PY_TEMPLATE.
- `py_indent`: indentation used in the Python file. (default: 4 spaces)

For example when using our Quick usage grammar, this is the output when running `my_grammar.export_py()`:
```python
"""
This grammar is generated using the Grammar.export_py() method and
should be used with the pyleri python module.

Source class: MyGrammar
Created at: 2017-03-14 19:14:51
"""
import re
from pyleri import Sequence
from pyleri import Keyword
from pyleri import Grammar
from pyleri import Regex

class MyGrammar(Grammar):

RE_KEYWORDS = re.compile('^\\w+')
r_name = Regex('^(?:"(?:[^"]*)")+')
k_hi = Keyword('hi')
START = Sequence(
k_hi,
r_name
)
```
## Elements
Pyleri has several elements which can be used to create a grammar.

### Keyword
syntax:
```python
Keyword(keyword, ign_case=Fasle)
```
The parser needs to match the keyword which is just a string. When matching keywords we need to tell the parser what characters are allowed in keywords. By default Pyleri uses `^\w+` which is both in Python and JavaScript equal to `^[A-Za-z0-9_]+`. We can overwrite the default by setting `RE_KEYWORDS` in the grammar. Keyword() accepts one keyword argument `ign_case` to tell the parser if we should match case insensitive.

Example:

```python
class TicTacToe(Grammar):
# Let's allow keywords with alphabetic characters and dashes.
RE_KEYWORDS = re.compile('^[A-Za-z-]+')

START = Keyword('tic-tac-toe', ign_case=True)

ttt_grammar = TicTacToe()
ttt_grammar.parse('Tic-Tac-Toe').is_valid # => True
```

### Regex
syntax:
```python
Regex(pattern, flags=0)
```
The parser compiles a regular expression using the `re` module. The current version of pyleri has only support for the `re.IGNORECASE` flag.
See the [Quick usage](#quick-usage) example for how to use `Regex`.

### Token
syntax:
```python
Token(token)
```
A token can be one or more characters and is usually used to match operators like `+`, `-`, `//` and so on. When we parse a string object where pyleri expects an element, it will automatically be converted to a `Token()` object.

Example:
```python
class Ni(Grammar):
t_dash = Token('-')
# We could just write delimiter='-' because
# any string will be converted to Token()
START = List(Keyword('ni'), delimiter=t_dash)

ni = Ni()
ni.parse('ni-ni-ni-ni-ni').is_valid # => True
```

### Tokens
syntax:
```python
Tokens(tokens)
```
Can be used to register multiple tokens at once. The `tokens` argument should be a string with tokens separated by spaces. If given tokens are different in size the parser will try to match the longest tokens first.

Example:
```python
class Ni(Grammar):
tks = Tokens('+ - !=')
START = List(Keyword('ni'), delimiter=tks)

ni = Ni()
ni.parse('ni + ni != ni - ni').is_valid # => True
```

### Sequence
syntax:
```python
Sequence(element, element, ...)
```
The parser needs to match each element in a sequence.

Example:
```python
class TicTacToe(Grammar):
START = Sequence(Keyword('Tic'), Keyword('Tac'), Keyword('Toe'))

ttt_grammar = TicTacToe()
ttt_grammar.parse('Tic Tac Toe').is_valid # => True
```

### Choice
syntax:
```python
Choice(element, element, ..., most_greedy=True)
```
The parser needs to choose between one of the given elements. Choice accepts one keyword argument `most_greedy` which is `True` by default. When `most_greedy` is set to `False` the parser will stop at the first match. When `True` the parser will try each element and returns the longest match. Setting `most_greedy` to `False` can provide some extra performance. Note that the parser will try to match each element in the exact same order they are parsed to Choice.

Example: let us use `Choice` to modify the Quick usage example to allow the string 'bye "Iris"'
```python
class MyGrammar(Grammar):
r_name = Regex('(?:"(?:[^"]*)")+')
k_hi = Keyword('hi')
k_bye = Keyword('bye')
START = Sequence(Choice(k_hi, k_bye), r_name)

my_grammar = MyGrammar()
my_grammar.parse('hi "Iris"').is_valid # => True
my_grammar.parse('bye "Iris"').is_valid # => True
```

### Repeat
syntax:
```python
Repeat(element, mi=0, ma=None)
```
The parser needs at least `mi` elements and at most `ma` elements. When `ma` is set to `None` we allow unlimited number of elements. `mi` can be any integer value equal or higher than 0 but not larger then `ma`.

Example:
```python
class Ni(Grammar):
START = Repeat(Keyword('ni'))

ni = Ni()
ni.parse('ni ni ni ni ni').is_valid # => True
```

It is not allowed to bind a name to the same element twice and Repeat(element, 1, 1) is a common solution to bind the element a second (or more) time(s).

For example consider the following:
```python
class MyGrammar(Grammar):
r_name = Regex('(?:"(?:[^"]*)")+')

# Raises a SyntaxError because we try to bind a second time.
r_address = r_name # WRONG

# Instead use Repeat
r_address = Repeat(r_name, 1, 1) # RIGHT
```

### List
syntax:
```python
List(element, delimiter=',', mi=0, ma=None, opt=False)
```
List is like Repeat but with a delimiter. A comma is used as default delimiter but any element is allowed. When a string is used as delimiter it will be converted to a `Token` element. `mi` and `ma` work exactly like with Repeat. An optional keyword argument `opt` can be set to `True` to allow the list to end with a delimiter. By default this is set to `False` which means the list has to end with an element.

Example:
```python
class Ni(Grammar):
START = List(Keyword('ni'))

ni = Ni()
ni.parse('ni, ni, ni, ni, ni').is_valid # => True
```

### Optional
syntax:
```python
Optional(element)
```
The parser looks for an optional element. It is like using `Repeat(element, 0, 1)` but we encourage to use `Optional` since it is more readable. (and slightly faster)

Example:
```python
class MyGrammar(Grammar):
r_name = Regex('(?:"(?:[^"]*)")+')
k_hi = Keyword('hi')
START = Sequence(k_hi, Optional(r_name))

my_grammar = MyGrammar()
my_grammar.parse('hi "Iris"').is_valid # => True
my_grammar.parse('hi').is_valid # => True
```

### Ref
syntax:
```python
Ref()
```
The grammar can make a forward reference to make recursion possible. In the example below we create a forward reference to START but note that
a reference to any element can be made.

>Warning: A reference is not protected against testing the same position in
>in a string. This could potentially lead to an infinite loop.
>For example:
>```python
>r = Ref()
>r = Optional(r) # DON'T DO THIS
>```
>Use [Prio](#prio) if such recursive construction is required.

Example:
```python
class NestedNi(Grammar):
START = Ref()
ni_item = Choice(Keyword('ni'), START)
START = Sequence('[', List(ni_item), ']')

nested_ni = NestedNi()
nested_ni.parse('[ni, ni, [ni, [], [ni, ni]]]').is_valid # => True
```

### Prio
syntax:
```python
Prio(element, element, ...)
```
Choose the first match from the prio elements and allow `THIS` for recursive operations. With `THIS` we point to the `Prio` element. Probably the example below explains how `Prio` and `THIS` can be used.

>Note: Use a [Ref](#ref) when possible.
>A `Prio` element is required when the same position in a string is potentially
>checked more than once.

Example:
```python
class Ni(Grammar):
k_ni = Keyword('ni')
START = Prio(
k_ni,
# '(' and ')' are automatically converted to Token('(') and Token(')')
Sequence('(', THIS, ')'),
Sequence(THIS, Keyword('or'), THIS),
Sequence(THIS, Keyword('and'), THIS))

ni = Ni()
ni.parse('(ni or ni) and (ni or ni)').is_valid # => True
```