add peg

peg/src/main.rs

@@ -0,0 +1,52 @@
+peg::parser!{
+    grammar list_parser() for str {
+      rule number() -> u32
+        = n:$(['0'..='9']+) { n.parse().unwrap() }
+      
+      pub rule list() -> Vec<u32>
+        = "[" l:number() ** "," "]" { l }
+    }
+}
+
+pub trait Node : std::fmt::Debug { fn eval(&self) -> i64; }
+
+#[derive(Debug)]
+struct NumberNode { val: i64, }
+impl Node for NumberNode {
+    fn eval(&self) -> i64 { self.val }
+}
+
+#[derive(Debug)]
+struct AddNode { left: Box<dyn Node>, right: Box<dyn Node>, }
+impl Node for AddNode {
+    fn eval(&self) -> i64 { self.left.eval() + self.right.eval() }
+}
+
+#[derive(Debug)]
+struct SubNode { left: Box<dyn Node>, right: Box<dyn Node>, }
+impl Node for SubNode {
+    fn eval(&self) -> i64 { self.left.eval() - self.right.eval() }
+}
+
+peg::parser!{
+    grammar expression() for str {
+        rule number() -> Box<dyn Node>
+            = n:$(['0'..='9']+) { Box::new(NumberNode{ val: n.parse().unwrap() }) }
+
+        pub rule calculate() -> Box<dyn Node> = precedence!{
+            x:(@) "+" y:@ { Box::new(AddNode{ left: x, right: y, }) }
+            x:(@) "-" y:@ { Box::new(SubNode{ left: x, right: y, }) }
+            --
+            "(" v:calculate() ")" { v }
+            n:number() {n}
+        }
+    }
+}
+
+fn main() {
+    println!("{:?}", list_parser::list("[1,1,2,3,5,8]"));
+
+    let a = expression::calculate("111+444-333");
+    println!("{:?}", a);
+    println!("{}", a.unwrap().eval());
+}