Initial commit with lexer

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/util.rs

@@ -0,0 +1,38 @@
+use std::{
+    fmt::{Display, Formatter, self},
+};
+
+pub struct LazyString<'f, F>
+    where F: Fn() -> String + 'f
+{
+    source: F,
+    _lifetime: std::marker::PhantomData<dyn Fn() + 'f>,
+}
+
+impl<'f, F> LazyString<'f, F>
+    where F: Fn() -> String + 'f
+{
+    pub fn new(source: F) -> Self {
+        LazyString {
+            source,
+            _lifetime: Default::default(),
+        }
+    }
+}
+
+impl<'f, F> Display for LazyString<'f, F>
+    where F: Fn() -> String + 'f
+{
+    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
+        let s = (self.source)();
+        Display::fmt(&s, fmt)
+    }
+}
+
+#[test]
+fn test_lazy_string() {
+    let i = 10;
+
+    let lzstr = LazyString::new(|| format!("the value is {}", i));
+    assert_eq!(lzstr.to_string(), "the value is 10");
+}