# Arcee
[](https://travis-ci.com/tdkihrr/arcee)
It is a Python parser generator, use EBNF-like syntax.
## Install
```bash
$ pip install Arcee
```
## Example
It's really readable.
grammar:
```
KEYWORDS : let, if, zero, -
NUMBER : \d+(\.\d*)?
ASSIGN : =
SUBTRACTION : -
RIGHT_BRACKET : (
COLON : ,
LETF_BRACKET : )
ID : [A-Za-z]+
SKIP : [ \\t]+
program : expression ;
expression : zeroexp
| diffexp
| ifexp
| varexp
| letexp
| constexp
;
constexp : $NUMBER ;
diffexp : '-' '(' expression ',' expression ')' ;
zeroexp : 'zero' '(' expression ')' ;
ifexp : 'if' expression 'then' expression 'else' expression ;
varexp : $ID ;
letexp : 'let' $ID '=' expression 'in' expression ;
```
```
$ arcee grammar > result.py
```
`result.py` has three parts:
### Token
```python
from collections import namedtuple
Token = namedtuple('Token', ['type', 'value', 'line', 'column'])
Program = namedtuple('Program', ['expression'])
# ...
```
### Lexer
```python
import re
def tokenize(code):
pass # ...
```
### Parser
```python
class Parser:
def __init__(self, token_list):
pass
# ...
def parse_expression(self):
if xxx:
self.parse_constexp()
elif yyy:
self.parse_diffexp()
#...
def parse_constexp(self):
pass
def parse_diffexp(self):
pass
def parse_zeroexp(self):
pass
def parse_ifexp(self):
pass
def parse_varexp(self):
pass
def parse_letexp(self):
pass
```
You can parse input such as:
```python
input = '''let a = 0 in if zero(a) then -(a, 1) else -(a, 2)'''
tokens = list(tokenize(input))
parser = Parser(tokens)
parser.parse_program()
```
result is:
```python
result = Program(
expression=Expression(
nonterminal=Letexp(
ID=Token(type='ID', value='a', line=2, column=4),
expression1=Expression(
nonterminal=Constexp(
NUMBER=Token(type='NUMBER', value='0', line=2, column=8))),
expression2=Expression(
nonterminal=Ifexp(
expression1=Expression(
nonterminal=Zeroexp(
expression=Expression(
nonterminal=Varexp(
ID=Token(type='ID', value='a', line=2, column=21))))),
expression2=Expression(
nonterminal=Diffexp(
expression1=Expression(
nonterminal=Varexp(
ID=Token(type='ID', value='a', line=2, column=31))),
expression2=Expression(
nonterminal=Constexp(
NUMBER=Token(type='NUMBER', value='1', line=2,
column=34))))),
expression3=Expression(
nonterminal=Diffexp(
expression1=Expression(
nonterminal=Varexp(
ID=Token(type='ID', value='a', line=2, column=44))),
expression2=Expression(
nonterminal=Constexp(
NUMBER=Token(type='NUMBER', value='2', line=2,
column=47))))))))))
```
Now, you can use this ast to do what you like.
You can also use api in your Python file.
```python
from arcee import generate
grammar = '''KEYWORDS : let, if, zero, -
NUMBER : \d+(\.\d*)?
ASSIGN : =
SUBTRACTION : -
RIGHT_BRACKET : (
COLON : ,
LETF_BRACKET : )
ID : [A-Za-z]+
SKIP : [ \\t]+
program : expression ;
expression : zeroexp
| diffexp
| ifexp
| varexp
| letexp
| constexp
;
constexp : $NUMBER ;
diffexp : '-' '(' expression ',' expression ')' ;
zeroexp : 'zero' '(' expression ')' ;
ifexp : 'if' expression 'then' expression 'else' expression ;
varexp : $ID ;
letexp : 'let' $ID '=' expression 'in' expression ;'''
print(generate(grammar))
```
