evaluate a very basic query

rust/src/eval.rs

@@ -0,0 +1,28 @@
+use crate::parse::{Expression, Reference, Value};
+
+impl<'a> Expression<'a> {
+    pub fn evaluate(&'a self, context: &serde_json::Value) -> Result<serde_json::Value, String> {
+        match self {
+            Expression::Value(value) => value.evaluate(&context),
+            _ => Err("Unknown expression type".to_string()),
+        }
+    }
+}
+
+impl<'a> Value<'a> {
+    pub fn evaluate(&'a self, context: &serde_json::Value) -> Result<serde_json::Value, String> {
+        match self {
+            Value::Reference(reference) => reference.evaluate(&context),
+            _ => Err("Unknown value type".to_string()),
+        }
+    }
+}
+
+impl<'a> Reference<'a> {
+    pub fn evaluate(&'a self, context: &'a serde_json::Value) -> Result<serde_json::Value, String> {
+        match self {
+            Reference::At => Ok(context.clone()),
+            _ => Err("Unknown value type".to_string()),
+        }
+    }
+}

rust/src/lib.rs

@@ -1,17 +1,19 @@
+pub mod eval;
 pub mod parse;
 
 pub fn query_value(
     query_str: String,
-    _data: serde_json::Value,
-) -> Result<serde_json::Value, &'static str> {
-    let ast = parse::expr(&query_str);
-    dbg!(ast);
-    Err("unimplemented")
+    data: serde_json::Value,
+) -> Result<serde_json::Value, String> {
+    match parse::expr(&query_str) {
+        Ok((_, ast)) => ast.evaluate(&data),
+        Err(err) => Err(err.to_string()),
+    }
 }
 
-pub fn query(query_str: String, data_str: String) -> Result<serde_json::Value, &'static str> {
+pub fn query(query_str: String, data_str: String) -> Result<serde_json::Value, String> {
     match serde_json::from_str(&data_str) {
         Ok(data) => query_value(query_str, data),
-        Err(_) => Err("Invalid JSON data"),
+        Err(_) => Err("Invalid JSON data".to_string()),
     }
 }

rust/src/main.rs

@@ -1,5 +1,5 @@
 fn main() {
-    let query = "count @".to_string();
+    let query = "@".to_string();
     let data = r#"
 { "foo": "bar" }
 "#