Add support for scientific notation of the form <coefficient>e{+,-,}<exponent>

src/token/mod.rs

@@ -354,9 +354,27 @@ fn partial_tokens_to_tokens(mut tokens: &[PartialToken]) -> EvalexprResult<Vec<T
                         Some(Token::Float(number))
                     } else if let Ok(boolean) = literal.parse::<bool>() {
                         Some(Token::Boolean(boolean))
+                    } else {
+                        // If there are two tokens following this one, check if the next one is
+                        // a plus or a minus. If so, then attempt to parse all three tokens as a
+                        // scientific notation number of the form `<coefficient>e{+,-}<exponent>`,
+                        // for example [Literal("10e"), Minus, Literal("3")] => "1e-3".parse().
+                        match (second, third) {
+                            (Some(s), Some(t))
+                                if s == PartialToken::Minus || s == PartialToken::Plus =>
+                            {
+                                if let Ok(number) =
+                                    format!("{}{}{}", literal, s, t).parse::<FloatType>()
+                                {
+                                    cutoff = 3;
+                                    Some(Token::Float(number))
                                 } else {
                                     Some(Token::Identifier(literal.to_string()))
                                 }
+                            }
+                            _ => Some(Token::Identifier(literal.to_string())),
+                        }
+                    }
                 },
                 PartialToken::Whitespace => {
                     cutoff = 1;

tests/integration.rs

@@ -17,6 +17,11 @@ fn test_unary_examples() {
     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)));
+    assert_eq!(eval("1e0"), Ok(Value::Float(1.0)));
+    assert_eq!(eval("1e-0"), Ok(Value::Float(1.0)));
+    assert_eq!(eval("10e3"), Ok(Value::Float(10000.0)));
+    assert_eq!(eval("10e+3"), Ok(Value::Float(10000.0)));
+    assert_eq!(eval("10e-3"), Ok(Value::Float(0.01)));
 }
 
 #[test]
@@ -41,6 +46,8 @@ fn test_binary_examples() {
     assert_eq!(eval("3+-1"), Ok(Value::Int(2)));
     assert_eq!(eval("-3-5"), Ok(Value::Int(-8)));
     assert_eq!(eval("-5--3"), Ok(Value::Int(-2)));
+    assert_eq!(eval("5e2--3"), Ok(Value::Float(503.0)));
+    assert_eq!(eval("-5e-2--3"), Ok(Value::Float(2.95)));
 }
 
 #[test]