1 files changed, 24 insertions, 0 deletions
diff --git a/src/def_rules.rs b/src/def_rules.rs
new file mode 100644
index 0000000..a2ba36e
--- /dev/null
+++ b/src/def_rules.rs
@@ -0,0 +1,24 @@
+use crate::sexpr::{self, Atom, Expr};
+
+#[derive(Debug, Clone)]
+pub struct Rule {
+    pub lhs: Expr,
+    pub rhs: Expr
+}
+
+impl TryFrom<Expr> for Rule {
+    type Error = ();
+    fn try_from(value: Expr) -> Result<Self, Self::Error> {
+        if let Expr::Application(v) = value && v[0] == Expr::Atom(Atom::Builtin(String::from("def-rule"))) && v.len() == 3 {
+            Ok(Rule {
+                lhs: v[1].clone(),
+                rhs: v[2].clone()
+            })
+        } else {Err(())}
+    }
+}
+
+pub fn parse_def_rules(input: String) -> Vec<Rule> {
+    let exprs = sexpr::Parser::new(&input).parse_all();
+    exprs.iter().filter_map(|e| e.clone().try_into().ok()).collect()
+}