WIP

README.txt

@@ -85,20 +85,27 @@ expressions and store variables:
     from sly import Lexer, Parser
 
     class CalcLexer(Lexer):
-        tokens = { NAME, NUMBER }
+        tokens = { NAME, NUMBER, PLUS, TIMES, MINUS, DIVIDE, ASSIGN, LPAREN, RPAREN }
         ignore = ' \t'
-        literals = { '=', '+', '-', '*', '/', '(', ')' }
 
         # Tokens
         NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
+        NUMBER = r'\d+'
 
-        @_(r'\d+')
+        # Special symbols
-        def NUMBER(self, t):
+        PLUS = r'\+'
-            t.value = int(t.value)
+        MINUS = r'-'
-            return t
+        TIMES = r'\*'
+        DIVIDE = r'/'
+        ASSIGN = r'='
+        LPAREN = r'\('
+        RPAREN = r'\)'
 
-        @_(r'\n+')
+        # Ignored pattern
-        def newline(self, t):
+        ignore_newline = r'\n+'
+
+        # Extra action for newlines
+        def ignore_newline(self, t):
             self.lineno += t.value.count('\n')
 
         def error(self, t):
@@ -109,15 +116,15 @@ expressions and store variables:
         tokens = CalcLexer.tokens
 
         precedence = (
-            ('left', '+', '-'),
+            ('left', PLUS, MINUS),
-            ('left', '*', '/'),
+            ('left', TIMES, DIVIDE),
-            ('right', 'UMINUS'),
+            ('right', UMINUS),
             )
 
         def __init__(self):
             self.names = { }
 
-        @_('NAME "=" expr')
+        @_('NAME ASSIGN expr')
         def statement(self, p):
             self.names[p.NAME] = p.expr
 
@@ -125,27 +132,27 @@ expressions and store variables:
         def statement(self, p):
             print(p.expr)
 
-        @_('expr "+" expr')
+        @_('expr PLUS expr')
         def expr(self, p):
             return p.expr0 + p.expr1
 
-        @_('expr "-" expr')
+        @_('expr MINUS expr')
         def expr(self, p):
             return p.expr0 - p.expr1
 
-        @_('expr "*" expr')
+        @_('expr TIMES expr')
         def expr(self, p):
             return p.expr0 * p.expr1
 
-        @_('expr "/" expr')
+        @_('expr DIVIDE expr')
         def expr(self, p):
             return p.expr0 / p.expr1
 
-        @_('"-" expr %prec UMINUS')
+        @_('MINUS expr %prec UMINUS')
         def expr(self, p):
             return -p.expr
 
-        @_('"(" expr ")"')
+        @_('LPAREN expr RPAREN')
         def expr(self, p):
             return p.expr
 
@@ -158,7 +165,7 @@ expressions and store variables:
             try:
                 return self.names[p.NAME]
             except LookupError:
-                print("Undefined name '%s'" % p.NAME)
+                print(f'Undefined name {p.NAME!r}')
                 return 0
 
     if __name__ == '__main__':

example/calc/calc.py

@@ -3,32 +3,32 @@
 # -----------------------------------------------------------------------------
 
 import sys
-sys.path.insert(0, "../..")
+sys.path.append('../..')
 
 from sly import Lexer, Parser
 
 class CalcLexer(Lexer):
-    # Set of token names.   This is always required
+    tokens = { NAME, NUMBER, PLUS, TIMES, MINUS, DIVIDE, ASSIGN, LPAREN, RPAREN }
-    tokens = { NUMBER, PLUS, MINUS, TIMES, DIVIDE, LPAREN, RPAREN }
-
-    # String containing ignored characters between tokens
     ignore = ' \t'
 
-    # Regular expression rules for tokens
+    # Tokens
+    NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
+    NUMBER = r'\d+'
+
+    # Special symbols
     PLUS = r'\+'
     MINUS = r'-'
     TIMES = r'\*'
     DIVIDE = r'/'
+    ASSIGN = r'='
     LPAREN = r'\('
     RPAREN = r'\)'
 
-    @_(r'\d+')
+    # Ignored pattern
-    def NUMBER(self, t):
+    ignore_newline = r'\n+'
-        t.value = int(t.value)
-        return t
 
-    @_(r'\n+')
+    # Extra action for newlines
-    def newline(self, t):
+    def ignore_newline(self, t):
         self.lineno += t.value.count('\n')
 
     def error(self, t):
@@ -36,50 +36,68 @@ class CalcLexer(Lexer):
         self.index += 1
 
 class CalcParser(Parser):
-    # Get the token list from the lexer (required)
     tokens = CalcLexer.tokens
 
-    # Grammar rules and actions
+    precedence = (
-    @_('expr PLUS term')
+        ('left', PLUS, MINUS),
+        ('left', TIMES, DIVIDE),
+        ('right', UMINUS)
+        )
+
+    def __init__(self):
+        self.names = { }
+
+    @_('NAME ASSIGN expr')
+    def statement(self, p):
+        self.names[p.NAME] = p.expr
+
+    @_('expr')
+    def statement(self, p):
+        print(p.expr)
+
+    @_('expr PLUS expr')
     def expr(self, p):
-        return p.expr + p.term
+        return p.expr0 + p.expr1
 
-    @_('expr MINUS term')
+    @_('expr MINUS expr')
     def expr(self, p):
-        return p.expr - p.term
+        return p.expr0 - p.expr1
 
-    @_('term')
+    @_('expr TIMES expr')
     def expr(self, p):
-        return p.term
+        return p.expr0 * p.expr1
 
-    @_('term TIMES factor')
+    @_('expr DIVIDE expr')
-    def term(self, p):
+    def expr(self, p):
-        return p.term * p.factor
+        return p.expr0 / p.expr1
 
-    @_('term DIVIDE factor')
+    @_('MINUS expr %prec UMINUS')
-    def term(self, p):
+    def expr(self, p):
-        return p.term / p.factor
+        return -p.expr
-
-    @_('factor')
-    def term(self, p):
-        return p.factor
-
-    @_('NUMBER')
-    def factor(self, p):
-        return p.NUMBER
 
     @_('LPAREN expr RPAREN')
-    def factor(self, p):
+    def expr(self, p):
         return p.expr
 
+    @_('NUMBER')
+    def expr(self, p):
+        return int(p.NUMBER)
+
+    @_('NAME')
+    def expr(self, p):
+        try:
+            return self.names[p.NAME]
+        except LookupError:
+            print(f'Undefined name {p.NAME!r}')
+            return 0
+
 if __name__ == '__main__':
     lexer = CalcLexer()
     parser = CalcParser()
-
     while True:
         try:
             text = input('calc > ')
-            result = parser.parse(lexer.tokenize(text))
-            print(result)
         except EOFError:
             break
+        if text:
+            parser.parse(lexer.tokenize(text))