Implemented configuration

src/configuration/mod.rs

@@ -1,13 +1,22 @@
 use crate::{error::Error, value::Value};
+use std::collections::HashMap;
 
 pub trait Configuration {
-    fn get_value(&self, identifier: &str) -> Result<Value, Error>;
+    fn get_value(&self, identifier: &str) -> Option<&Value>;
 }
 
 pub struct EmptyConfiguration;
 
 impl Configuration for EmptyConfiguration {
-    fn get_value(&self, _identifier: &str) -> Result<Value, Error> {
-        Err(Error::IdentifierNotFound)
+    fn get_value(&self, identifier: &str) -> Option<&Value> {
+        None
     }
 }
+
+pub type HashMapConfiguration = HashMap<String, Value>;
+
+impl Configuration for HashMapConfiguration {
+    fn get_value(&self, identifier: &str) -> Option<&Value> {
+        self.get(identifier)
+    }
+}

src/error/mod.rs

@@ -29,7 +29,7 @@ pub enum Error {
     PrecedenceViolation,
 
     /// An identifier operation did not find its value in the configuration.
-    IdentifierNotFound,
+    IdentifierNotFound(String),
 
     /// A value has the wrong type.
     TypeError,

src/lib.rs

@@ -24,7 +24,7 @@ mod test {
         assert_eq!(eval("3.3"), Ok(Value::Float(3.3)));
         assert_eq!(eval("true"), Ok(Value::Boolean(true)));
         assert_eq!(eval("false"), Ok(Value::Boolean(false)));
-        assert_eq!(eval("blub"), Err(Error::IdentifierNotFound));
+        assert_eq!(eval("blub"), Err(Error::IdentifierNotFound("blub".to_string())));
         assert_eq!(eval("-3"), Ok(Value::Int(-3)));
         assert_eq!(eval("-3.6"), Ok(Value::Float(-3.6)));
         assert_eq!(eval("----3"), Ok(Value::Int(3)));

src/operator/mod.rs

@@ -479,6 +479,10 @@ impl Operator for Identifier {
     fn eval(&self, arguments: &[Value], configuration: &Configuration) -> Result<Value, Error> {
         expect_argument_amount(arguments.len(), 0)?;
 
-        configuration.get_value(&self.identifier)
+        if let Some(value) = configuration.get_value(&self.identifier).cloned() {
+            Ok(value)
+        } else {
+            Err(Error::IdentifierNotFound(self.identifier.clone()))
+        }
     }
 }