Rename Node::eval to Node::eval_with_configuration for consistency.

* Rename `Node::eval` to `Node::eval_with_configuration`
 + Add `Node::eval` that calls `Node::eval_with_configuration` with an `EmptyConfiguration`
 + Improve documentation of `Node` and the changed methods

Implements #5

src/lib.rs

@@ -69,10 +69,10 @@
 //! configuration.insert_variable("a", 6);
 //! configuration.insert_variable("b", 2);
 //! configuration.insert_variable("c", 3);
-//! assert_eq!(precompiled.eval(&configuration), Ok(Value::from(true)));
+//! assert_eq!(precompiled.eval_with_configuration(&configuration), Ok(Value::from(true)));
 //!
 //! configuration.insert_variable("c", 8);
-//! assert_eq!(precompiled.eval(&configuration), Ok(Value::from(false)));
+//! assert_eq!(precompiled.eval_with_configuration(&configuration), Ok(Value::from(false)));
 //! ```
 //!
 //! ## Features
@@ -234,7 +234,7 @@ pub use value::Value;
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval(string: &str) -> Result<Value, Error> {
-    tree::tokens_to_operator_tree(token::tokenize(string)?)?.eval(&EmptyConfiguration)
+    eval_with_configuration(string, &EmptyConfiguration)
 }
 
 /// Evaluate the given expression string with the given configuration.
@@ -256,7 +256,7 @@ pub fn eval_with_configuration(
     string: &str,
     configuration: &Configuration,
 ) -> Result<Value, Error> {
-    tree::tokens_to_operator_tree(token::tokenize(string)?)?.eval(configuration)
+    tree::tokens_to_operator_tree(token::tokenize(string)?)?.eval_with_configuration(configuration)
 }
 
 /// Build the operator tree for the given expression string.
@@ -276,10 +276,10 @@ pub fn eval_with_configuration(
 /// configuration.insert_variable("two", 2);
 /// configuration.insert_variable("three", 3);
 ///
-/// assert_eq!(precomputed.eval(&configuration), Ok(Value::from(6)));
+/// assert_eq!(precomputed.eval_with_configuration(&configuration), Ok(Value::from(6)));
 ///
 /// configuration.insert_variable("three", 5);
-/// assert_eq!(precomputed.eval(&configuration), Ok(Value::from(8)));
+/// assert_eq!(precomputed.eval_with_configuration(&configuration), Ok(Value::from(8)));
 /// ```
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*

src/tree/mod.rs

@@ -1,5 +1,6 @@
 use crate::{configuration::Configuration, error::Error, operator::*, value::Value};
 use token::Token;
+use EmptyConfiguration;
 
 mod display;
 
@@ -7,13 +8,17 @@ mod display;
 /// The operator tree is created by the crate-level `build_operator_tree` method.
 /// It can be evaluated for a given configuration with the `Node::eval` method.
 ///
+/// The advantage of constructing the operator tree separately from the actual evaluation is that it can be evaluated arbitrarily often with different configurations.
+///
 /// # Examples
 ///
 /// ```rust
 /// use evalexpr::*;
 ///
-/// let node = build_operator_tree("1 + 2").unwrap();
-/// assert_eq!(node.eval(&EmptyConfiguration), Ok(Value::from(3)));
+/// let mut configuration = HashMapConfiguration::new();
+/// configuration.insert_variable("alpha", 2);
+/// let node = build_operator_tree("1 + alpha").unwrap();
+/// assert_eq!(node.eval_with_configuration(&configuration), Ok(Value::from(3)));
 /// ```
 ///
 #[derive(Debug)]
@@ -34,17 +39,24 @@ impl Node {
         Self::new(RootNode)
     }
 
-    /// Evaluates the operator tree rooted at this node.
+    /// Evaluates the operator tree rooted at this node with the given configuration.
     ///
-    /// Fails, if an operator is used with a wrong number of arguments or a wrong type.
-    pub fn eval(&self, configuration: &Configuration) -> Result<Value, Error> {
+    /// Fails, if one of the operators in the expression tree fails.
+    pub fn eval_with_configuration(&self, configuration: &Configuration) -> Result<Value, Error> {
         let mut arguments = Vec::new();
         for child in self.children() {
-            arguments.push(child.eval(configuration)?);
+            arguments.push(child.eval_with_configuration(configuration)?);
         }
         self.operator().eval(&arguments, configuration)
     }
 
+    /// Evaluates the operator tree rooted at this node with an empty configuration.
+    ///
+    /// Fails, if one of the operators in the expression tree fails.
+    pub fn eval(&self) -> Result<Value, Error> {
+        self.eval_with_configuration(&EmptyConfiguration)
+    }
+
     fn children(&self) -> &[Node] {
         &self.children
     }