Implement a very basic first stab at lisp parser.

src/compare/error.rs

@@ -0,0 +1,25 @@
+use nom::error::ErrorKind;
+use nom::error::ParseError;
+use nom::IResult;
+
+pub type Res<T, U> = IResult<T, U, CustomError<T>>;
+
+#[derive(Debug, PartialEq)]
+pub enum CustomError<I> {
+    MyError(MyError<I>),
+    Nom(I, ErrorKind),
+}
+
+#[derive(Debug, PartialEq)]
+pub struct MyError<I>(pub I);
+
+impl<I> ParseError<I> for CustomError<I> {
+    fn from_error_kind(input: I, kind: ErrorKind) -> Self {
+        CustomError::Nom(input, kind)
+    }
+
+    fn append(_input: I, _kind: ErrorKind, mut other: Self) -> Self {
+        // Doesn't do append like VerboseError
+        other
+    }
+}