1 files changed, 41 insertions, 0 deletions
diff --git a/src/sexp/util.rs b/src/sexp/util.rs
index aa7ae18..db400e9 100644
--- a/src/sexp/util.rs
+++ b/src/sexp/util.rs
@@ -87,6 +87,47 @@ impl SExp {
         }
     }
 
+    pub fn get_vars_bound_by_pattern(&self) -> Vec<String> {
+	match self {
+	    Atom(Var(s)) => vec![s.clone()],
+	    Atom(RestPat(s)) => vec![s.clone()],
+	    SCons(a, b) =>
+		(*a).get_vars_bound_by_pattern()
+		.into_iter()
+		.chain((*b).get_vars_bound_by_pattern())
+		.collect(),
+	    _ => vec![],
+	}
+    }
+
+    pub fn get_case_scrut_pats_and_arms(self) ->
+	Option<(SExp, Vec<(SExp, SExp)>)> {
+	    let (scrutinee, patarms) = self.check_case()?;
+
+	    let scrutinee = match scrutinee {
+		SCons(q, v) if *q == Atom(Quote) || *q == Atom(Vector) => *v,
+		t => t,
+	    };
+
+	    let mut res = vec![];
+	    for patarm in patarms {
+		let (pat, arm) = match patarm {
+		    SCons(pat, arm) => Some((*pat, *arm)),
+		    _ => {
+			println!("warn: invalid structure in case arms,");
+			println!("      should be unreachable after type checking");
+			None
+		    },
+		}?;
+		let arm = match arm {
+		    SCons(x, n) if *n == Atom(Nil) => *x,
+		    t => t,
+		};
+		res.push((pat, arm));
+	    }
+	    Some((scrutinee, res))
+	}
+
     pub fn check_case(self) -> Option<(SExp, Vec<SExp>)> {
         match &(self.parts())[..] {
 	    [casekw, scrutinee, cases @ ..] if casekw.clone() == Atom(Case) =>