Add a human friendly grammar.

Author: hzhangxyz

g4/Ds.g4

@@ -0,0 +1,43 @@
+grammar Ds;
+
+rule_pool
+    : rule (NEWLINE+ rule)* EOF
+    ;
+
+rule
+    : term
+    | (term (',' term)*)? '->' term
+    ;
+
+term
+    : SYMBOL                                                 # symbol
+    | term '(' (term (',' term)*)? ')'                       # function
+    | '(' term ')'                                           # parentheses
+    | <assoc=right> ('~' | '!' | '-' | '+' | '&' | '*') term # unary
+    | term ('*' | '/' | '%') term                            # binary
+    | term ('+' | '-') term                                  # binary
+    | term ('<<' | '>>') term                                # binary
+    | term ('<' | '>' | '<=' | '>=') term                    # binary
+    | term ('==' | '!=') term                                # binary
+    | term '&' term                                          # binary
+    | term '^' term                                          # binary
+    | term '|' term                                          # binary
+    | term '&&' term                                         # binary
+    | term '||' term                                         # binary
+    ;
+
+WHITESPACE
+    : [ \t]+ -> skip
+    ;
+
+COMMENT
+    : '//' ~[\r\n]* -> skip
+    ;
+
+NEWLINE
+    : [\r\n]
+    ;
+
+SYMBOL
+    : ~[ \t\r\n,()]+
+    ;

g4/main.py

@@ -0,0 +1,45 @@
+from antlr4 import FileStream, CommonTokenStream
+from DsLexer import DsLexer
+from DsParser import DsParser
+from DsVisitor import DsVisitor
+
+
+class Visitor(DsVisitor):
+    def visitRule_pool(self, ctx: DsParser.Rule_poolContext):
+        return "\n\n".join([self.visit(r) for r in ctx.rule_()])
+
+    def visitRule(self, ctx: DsParser.RuleContext):
+        result = [self.visit(t) for t in ctx.term()]
+        if len(result) == 1:
+            return result[0]
+        else:
+            conclusion = result.pop()
+            length = max(len(premise) for premise in result)
+            result.append("-" * length)
+            result.append(conclusion)
+            return "\n".join(result)
+
+    def visitSymbol(self, ctx: DsParser.SymbolContext):
+        return ctx.SYMBOL().getText()
+
+    def visitFunction(self, ctx: DsParser.FunctionContext):
+        return f"(function {' '.join(self.visit(t) for t in ctx.term())})"
+
+    def visitParentheses(self, ctx: DsParser.ParenthesesContext):
+        return self.visit(ctx.term())
+
+    def visitUnary(self, ctx: DsParser.UnaryContext):
+        return f"(unary {ctx.getChild(0).getText()} {self.visit(ctx.term())})"
+
+    def visitBinary(self, ctx: DsParser.BinaryContext):
+        return f"(binary {ctx.getChild(1).getText()} {self.visit(ctx.term(0))} {self.visit(ctx.term(1))})"
+
+
+input_stream = FileStream("input.ds")
+lexer = DsLexer(input_stream)
+stream = CommonTokenStream(lexer)
+parser = DsParser(stream)
+tree = parser.rule_pool()
+visitor = Visitor()
+result = visitor.visit(tree)
+print(result)