Adds parser example

Author: Maxcode123

examples/parser.py

@@ -0,0 +1,49 @@
+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)