Add crate level shortcut evaluations for Value::Empty

Relates to #28

src/context/mod.rs

@@ -1,9 +1,9 @@
 use std::collections::HashMap;
 
-use EvalexprError;
-use EvalexprResult;
 use function::Function;
 use value::value_type::ValueType;
+use EvalexprError;
+use EvalexprResult;
 
 use crate::value::Value;
 

src/error/mod.rs

@@ -6,7 +6,7 @@
 //! They are meant as shortcuts to not write the same error checking code everywhere.
 
 use token::PartialToken;
-use value::{TupleType, value_type::ValueType};
+use value::{value_type::ValueType, TupleType};
 
 use crate::value::Value;
 

src/interface/mod.rs

@@ -1,14 +1,16 @@
+use token;
+use tree;
+use value::TupleType;
 use Context;
 use EmptyContext;
+use EmptyType;
 use EvalexprError;
 use EvalexprResult;
 use FloatType;
 use IntType;
 use Node;
-use token;
-use tree;
 use Value;
-use value::TupleType;
+use EMPTY_VALUE;
 
 /// Evaluate the given expression string.
 ///
@@ -134,6 +136,13 @@ pub fn eval_tuple(string: &str) -> EvalexprResult<TupleType> {
     eval_tuple_with_context(string, &EmptyContext)
 }
 
+/// Evaluate the given expression string into an empty value.
+///
+/// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
+pub fn eval_empty(string: &str) -> EvalexprResult<EmptyType> {
+    eval_empty_with_context(string, &EmptyContext)
+}
+
 /// Evaluate the given expression string into a string with the given context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
@@ -202,6 +211,17 @@ pub fn eval_tuple_with_context(string: &str, context: &Context) -> EvalexprResul
     }
 }
 
+/// Evaluate the given expression string into an empty value with the given context.
+///
+/// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
+pub fn eval_empty_with_context(string: &str, context: &Context) -> EvalexprResult<EmptyType> {
+    match eval_with_context(string, context) {
+        Ok(Value::Empty) => Ok(EMPTY_VALUE),
+        Ok(value) => Err(EvalexprError::expected_empty(value)),
+        Err(error) => Err(error),
+    }
+}
+
 /// Evaluate the given expression string into a string with the given mutable context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
@@ -278,3 +298,17 @@ pub fn eval_tuple_with_context_mut(
         Err(error) => Err(error),
     }
 }
+
+/// Evaluate the given expression string into an empty value with the given mutable context.
+///
+/// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
+pub fn eval_empty_with_context_mut(
+    string: &str,
+    context: &mut Context,
+) -> EvalexprResult<EmptyType> {
+    match eval_with_context_mut(string, context) {
+        Ok(Value::Empty) => Ok(EMPTY_VALUE),
+        Ok(value) => Err(EvalexprError::expected_empty(value)),
+        Err(error) => Err(error),
+    }
+}

src/lib.rs

@@ -283,7 +283,7 @@ pub use function::Function;
 pub use interface::*;
 pub use tree::Node;
 pub use value::{
-    EMPTY_VALUE, EmptyType, FloatType, IntType, TupleType, Value, value_type::ValueType,
+    value_type::ValueType, EmptyType, FloatType, IntType, TupleType, Value, EMPTY_VALUE,
 };
 
 mod context;

src/tree/mod.rs

@@ -1,9 +1,9 @@
+use token::Token;
+use value::{TupleType, EMPTY_VALUE};
 use EmptyContext;
 use EmptyType;
 use FloatType;
 use IntType;
-use token::Token;
-use value::{EMPTY_VALUE, TupleType};
 
 use crate::{
     context::Context,

tests/integration.rs

@@ -1,6 +1,6 @@
 extern crate evalexpr;
 
-use evalexpr::{*, error::*};
+use evalexpr::{error::*, *};
 
 #[test]
 fn test_unary_examples() {
@@ -362,6 +362,8 @@ fn test_shortcut_functions() {
         eval_tuple_with_context("3,3", &context),
         Ok(vec![Value::Int(3), Value::Int(3)])
     );
+    assert_eq!(eval_empty(""), Ok(EMPTY_VALUE));
+    assert_eq!(eval_empty_with_context("", &context), Ok(EMPTY_VALUE));
 
     // assert_eq!(build_operator_tree("???").unwrap().eval_string());
     assert_eq!(
@@ -433,6 +435,10 @@ fn test_shortcut_functions() {
         eval_tuple_with_context_mut("3,3", &mut context),
         Ok(vec![Value::Int(3), Value::Int(3)])
     );
+    assert_eq!(
+        eval_empty_with_context_mut("", &mut context),
+        Ok(EMPTY_VALUE)
+    );
 
     assert_eq!(
         build_operator_tree("string")