Updates README.md

README.md

@@ -8,6 +8,8 @@
 Python parser generator
 
 ## Quick start
+
+### Creating a parsing table
 ```py
 from syntactes import Grammar, Rule, SLRGenerator, Token
 
@@ -54,16 +56,86 @@ SLR PARSING TABLE
 -------------------------------------------------
 |     |  $   |  +   |  E   |  S   |  T   |  x  |
 -------------------------------------------------
-|  1  |  --  |  --  |  s3  |  --  |  s4  |  s2 |
+|  1  |  --  |  --  |  s4  |  --  |  s2  |  s3 |
 -------------------------------------------------
-|  2  |  r4  |  r4  |  --  |  --  |  --  |  -- |
+|  2  |  r2  |  s5  |  --  |  --  |  --  |  -- |
 -------------------------------------------------
-|  3  |  a  |  --  |  --  |  --  |  --  |  -- |
-------------------------------------------------
-|  4  |  r2  |  s5  |  --  |  --  |  --  |  -- |
+|  3  |  r4  |  r4  |  --  |  --  |  --  |  -- |
 -------------------------------------------------
-|  5  |  --  |  --  |  s6  |  --  |  s4  |  s2 |
+|  4  |  a  |  --  |  --  |  --  |  --  |  -- |
+------------------------------------------------
+|  5  |  --  |  --  |  s6  |  --  |  s2  |  s3 |
 -------------------------------------------------
 |  6  |  r1  |  --  |  --  |  --  |  --  |  -- |
 -------------------------------------------------
 ```
+
+### Parsing
+
+```py
+from syntactes import Grammar, Rule, Token
+from syntactes.parser import ParserError, SLRParser, execute_on
+
+EOF = Token.eof()
+S = Token("S", is_terminal=False)
+E = Token("E", False)
+T = Token("T", False)
+x = Token("x", True, 1)  # value of token is 1
+PLUS = Token("+", True)
+
+tokens = {EOF, S, E, T, x, PLUS}
+
+# 0. S -> E $
+# 1. E -> T + E
+# 2. E -> T
+# 3. T -> x
+rule_1 = Rule(0, S, E, EOF)
+rule_2 = Rule(1, E, T, PLUS, E)
+rule_3 = Rule(2, E, T)
+rule_4 = Rule(4, T, x)
+
+rules = (rule_1, rule_2, rule_3, rule_4)
+
+grammar = Grammar(rule_1, rules, tokens)
+
+parser = SLRParser.from_grammar(grammar)
+
+
+@execute_on(rule_4)
+def push_value(x_token):
+    # Add and argument for every token on the right-hand side of the rule.
+    print(
+        f"received token {x_token} with value: {x_token.value}, reducing by rule: {rule_4}"
+    )
+
+
+@execute_on(rule_2)
+def add(left, plus, right):
+    print(f"received tokens {left}, {plus}, {right}, reducing by rule: {rule_2}")
+
+
+print("Parsing stream: x + x + x $\n")
+parser.parse([x, PLUS, x, PLUS, x, EOF])
+
+print("\nParsing stream: x + $\n")
+try:
+    parser.parse([x, PLUS, EOF])
+except ParserError as e:
+    print("ParserError:", e)
+```
+
+Running the above example produces this output:
+```
+Parsing stream: x + x + x $
+
+received token x with value: 1, reducing by rule: T -> x
+received token x with value: 1, reducing by rule: T -> x
+received token x with value: 1, reducing by rule: T -> x
+received tokens E, +, T, reducing by rule: E -> T + E
+received tokens E, +, T, reducing by rule: E -> T + E
+
+Parsing stream: x + $
+
+received token x with value: 1, reducing by rule: T -> x
+ParserError: Received token: $; expected one of: ['x', 'T', 'E']
+```