enh(generic-snmp): Average added to the parser

experimental/src/grammar.lalrpop

@@ -14,9 +14,22 @@ pub Product: f32 = {
     <t:Term> => t,
 };
 
+pub Args = Comma<Sum>; // (0)
+
+Comma<T>: Vec<f32> = { // (1)
+    <mut v:(<T> ",")*> <e:T?> => match e { // (2)
+        None => v,
+        Some(e) => {
+            v.push(e);
+            v
+        }
+    }
+};
+
 pub Term: f32 = {
     <n:Num> => n,
     "(" <t:Sum> ")" => t,
+    "Average" "(" <a:Args> ")" => { let sum:f32 = a.iter().sum(); sum / a.len() as f32 }
 };
 
 Num: f32 = <s:r"-?[0-9.]+"> => f32::from_str(s).unwrap();

experimental/src/main.rs

@@ -136,4 +136,15 @@ mod Test {
         assert!(res.is_ok());
         assert!(res.unwrap() == 4_f32);
     }
+
+    #[test]
+    fn function() {
+        let res = grammar::TermParser::new().parse("Average(1, 2, 3)");
+        assert!(res.is_ok());
+        assert!(res.unwrap() == 2_f32);
+
+        let res = grammar::TermParser::new().parse("Average(1 + 2 * 2, 3, 4)");
+        assert!(res.is_ok());
+        assert!(res.unwrap() == 4_f32);
+    }
 }