Adding prob7, unfinished.

src/prob7.rs

@@ -0,0 +1,17 @@
+use nom::{branch::alt, bytes::complete::tag, combinator::map, IResult};
+
+use crate::prob7::Instructions::{Cd, Dir, Ls};
+
+enum Instructions {
+    Ls,
+    Cd,
+    Dir,
+}
+
+fn parse_instruction(i: &str) -> IResult<&str, Instructions> {
+    alt((
+        map(tag("ls"), |_| Ls),
+        map(tag("cd"), |_| Cd),
+        map(tag("dir"), |_| Dir),
+    ))(i)
+}