1 files changed, 50 insertions, 0 deletions
diff --git a/src/chomp/check/closed.rs b/src/chomp/check/closed.rs
new file mode 100644
index 0000000..07ef7ac
--- /dev/null
+++ b/src/chomp/check/closed.rs
@@ -0,0 +1,50 @@
+use super::super::{
+    ast::{Alt, Call, Cat, Epsilon, Fix, Literal, Parameter, Variable},
+    visit::{Visitable, Visitor},
+};
+
+/// Test if term is closed for a context with `depth` variables.
+#[derive(Copy, Clone, Debug, Default)]
+pub struct Closed {
+    depth: usize,
+    params: usize,
+}
+
+impl Visitor for Closed {
+    type Out = bool;
+
+    fn visit_epsilon(&mut self, _eps: &Epsilon) -> Self::Out {
+        true
+    }
+
+    fn visit_literal(&mut self, _lit: &Literal) -> Self::Out {
+        true
+    }
+
+    fn visit_cat(&mut self, cat: &Cat) -> Self::Out {
+        cat.first().visit(self) && cat.second().visit(self)
+    }
+
+    fn visit_alt(&mut self, alt: &Alt) -> Self::Out {
+        alt.left().visit(self) && alt.right().visit(self)
+    }
+
+    fn visit_fix(&mut self, fix: &Fix) -> Self::Out {
+        self.depth += 1;
+        let res = fix.inner().visit(self);
+        self.depth -= 1;
+        res
+    }
+
+    fn visit_variable(&mut self, var: &Variable) -> Self::Out {
+        var.index() < self.depth
+    }
+
+    fn visit_parameter(&mut self, param: &Parameter) -> Self::Out {
+        param.index() < self.params
+    }
+
+    fn visit_call(&mut self, call: &Call) -> Self::Out {
+        call.args().iter().all(|arg| arg.visit(self))
+    }
+}