add a crate 'tokens'

This crate is responsible for the users to conveniently define their
own tokenizers.  Right now the user has to tokenize the input string
manually, which is not quite what is expected from a parser, from the
view point of users.

1 files changed, 20 insertions, 0 deletions

diff --git a/tokens/src/lib.rs b/tokens/src/lib.rs
new file mode 100644
index 0000000..ba4f7ac
--- /dev/null
+++ b/tokens/src/lib.rs
@@ -0,0 +1,20 @@
+//! This package defines the trait for tokenizers that are expected
+//! from the parser.
+//!
+//! This is not the essential part of the package, and users might
+//! want to tweak this part.
+
+pub fn add(left: usize, right: usize) -> usize {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}