3 files changed, 44 insertions, 1 deletions

diff --git a/src/sexp/display.rs b/src/sexp/display.rs
index a978f61..5d78e93 100644
--- a/src/sexp/display.rs
+++ b/src/sexp/display.rs
@@ -29,6 +29,8 @@ impl fmt::Display for SLeaf {
             Vector => "vector".to_string(),
 	    Print  => "print".to_string(),
             Let    => "let".to_string(),
+	    Ty(t)  => t.to_string(),
+	    Arr    => "->".to_string(),
             Nil    => "()".to_string(),
         })
     }
diff --git a/src/sexp/mod.rs b/src/sexp/mod.rs
index 296553f..11c185f 100644
--- a/src/sexp/mod.rs
+++ b/src/sexp/mod.rs
@@ -4,6 +4,8 @@ pub mod util;
 pub mod subst;
 pub mod display;
 
+use crate::r#type::Type;
+
 /// A leaf node for S-Expressions.
 ///
 /// May represent built-in operators,
@@ -33,6 +35,9 @@ pub enum SLeaf {
 
     Let,
 
+    Ty(Type),
+    Arr,
+
     Print,
 
     Int(i32),
@@ -58,6 +63,7 @@ pub enum SExp {
 
 use SExp::*;
 use SLeaf::*;
+use crate::sexp::util::*;
 
 
 impl SExp {
@@ -71,7 +77,7 @@ impl SExp {
             SCons(a, b) =>
                 SCons(a.clone(), b.clone()).check_let().is_some() ||
                 (
-                    (**a == Atom(Quote) || **a == Atom(Vector))
+                    (**a == Atom(Quote) || **a == Atom(Vector) || (**a).is_type_lit())
                     && b.consists_of_values()
                 ),
             Atom(Var(_)) => false,
@@ -85,4 +91,15 @@ impl SExp {
             _ => false
         }
     }
+
+    pub fn is_type_lit(&self) -> bool {
+	match self {
+	    Atom(Ty(_)) => true,
+	    SCons(a, b) => scons(a.clone(), b.clone())
+		.parts()
+		.into_iter()
+		.all(|x| x.is_type_lit()),
+	    _ => false
+	}
+    }
 }
diff --git a/src/sexp/step.rs b/src/sexp/step.rs
index 11df257..c26dce9 100644
--- a/src/sexp/step.rs
+++ b/src/sexp/step.rs
@@ -1,5 +1,6 @@
 
 use crate::sexp::{SExp, SExp::*, SLeaf::*, util::*};
+use crate::r#type::{Type::*, util::*};
 
 impl SExp {
 
@@ -521,6 +522,29 @@ impl SExp {
                 }
             },
 
+	    // Type arrow
+	    SCons(op, l) if *op == Atom(Arr) => {
+                let ls = l.parts();
+                let t1 = ls.get(0).ok_or("wrong list length".to_string())?;
+                let t2 = ls.get(1).ok_or("wrong list length".to_string())?;
+                match (t1.clone().multistep()?, t2.clone().multistep()?) {
+                    (Atom(Ty(a)), Atom(Ty(b))) => Ok(Atom(Ty(arr(a.clone(), b.clone())))),
+                    _ => Err("invalid args".to_string()),
+                }
+	    },
+
+	    // Type list
+	    SCons(op, l) if (*op).is_type_lit() => {
+		let mut res = vec![];
+		for exp in std::iter::once(*op).chain(l.parts()) {
+		    res.push(match exp.multistep()? {
+			Atom(Ty(t)) => Ok(t),
+			e => Err(format!("not a type: {e}")),
+		    }?);
+		}
+		Ok(Atom(Ty(List(res))))
+	    },
+
 	    // Print
 	    SCons(op, l) if *op == Atom(Print) => {
 		println!("{}", *l);