arith a bit

.gitignore

@@ -0,0 +1,3 @@
+src/__pycache__
+src/parser.out
+src/parsetab.py

src/arithmetic.py

@@ -0,0 +1,80 @@
+import ply.yacc
+import ply.lex
+
+# scanner
+tokens = [
+    'NUMBER',
+    'EXP'
+]
+
+literals = ['+', '*', '(', ')']
+
+t_ignore = '\n\t '
+
+def t_error(t):
+    print(f"error: '{t}'")
+
+def t_NUMBER(t):
+    r'0|[1-9][0-9]*'
+    t.value = int(t.value)
+    return t
+
+def t_EXP(t):
+    r'\*\*'
+    pass
+
+lexer = ply.lex.lex()
+
+# parser
+start = 'start'
+
+def p_start(p):
+    "start : expr"
+    print(p[1])
+
+def p_expr_sum(p):
+    "expr : expr '+' prod"
+    p[0] = p[1] + p[3]
+    return p
+
+def p_expr_prod(p):
+    "expr : prod"
+    p[0] = p[1]
+    return p
+
+def p_prod_prod(p):
+    "prod : prod '*' pow"
+    p[0] = p[1] * p[3]
+    return p
+
+def p_prod_pow(p):
+    "prod : pow"
+    p[0] = p[1]
+    return p
+
+def p_pow_exp(p):
+    "pow : fac EXP pow"
+    p[0] = p[1] ** p[3]
+    return p
+
+def p_pow_fac(p):
+    "pow : fac"
+    p[0] = p[1]
+    return p
+
+def p_fac_inner(p):
+    "fac : '(' expr ')'"
+    p[0] = p[2]
+    return p
+
+def p_fac_num(p):
+    "fac : NUMBER"
+    p[0] = int(p[1])
+    return p
+
+parser = ply.yacc.yacc()
+while True:
+    s = input('calc> ')
+    ply.yacc.parse(s)
+    if s == '':
+        break