feat: fixed point dynamics

1 files changed, 38 insertions, 24 deletions

diff --git a/src/sexp/step.rs b/src/sexp/step.rs
index 5b60fec..84553e1 100644
--- a/src/sexp/step.rs
+++ b/src/sexp/step.rs
@@ -1,6 +1,5 @@
 
 use crate::sexp::{SExp, SExp::*, SLeaf::*, util::*};
-use crate::r#type::{Type::*, util::*};
 
 impl SExp {
 
@@ -346,6 +345,31 @@ impl SExp {
                 None => panic!("unreachable as per match guard arm"),
             },
 
+	    // Custom anonymous functions
+	    SCons(op, l) if (*op).is_fun() => {
+
+		// Get function parts
+		let ls = op.parts();
+		let argnames = ls.get(1).unwrap()
+		    .clone().parts();
+		let mut argnamevec = vec![];
+		for name in argnames.clone() {
+		    argnamevec.push(match name {
+			Atom(Var(s)) => Ok(s),
+			_ => Err("invalid entry in argument list (should be unreachable after type checker)".to_string()),
+		    }?);
+		}
+		let mut body = ls.get(4).unwrap().clone();
+
+		// Get argument parts
+		let suppliedargs = l.parts();
+		for (name, value) in argnamevec.into_iter().zip(suppliedargs) {
+		    body = body.subst(&name, &value);
+		}
+
+		Ok(body)
+	    },
+
 	    // case expressions
 	    SCons(op, l) if scons(op.clone(), l.clone()).check_case().is_some() => {
 		let (scrutinee, patarms) = scons(op, l).check_case().unwrap();
@@ -394,29 +418,19 @@ impl SExp {
             },
 
 
-	    // Custom anonymous functions
-	    SCons(op, l) if (*op).is_fun() => {
-
-		// Get function parts
-		let ls = op.parts();
-		let argnames = ls.get(1).unwrap()
-		    .clone().parts();
-		let mut argnamevec = vec![];
-		for name in argnames.clone() {
-		    argnamevec.push(match name {
-			Atom(Var(s)) => Ok(s),
-			_ => Err("invalid entry in argument list (should be unreachable after type checker)".to_string()),
-		    }?);
-		}
-		let mut body = ls.get(4).unwrap().clone();
-
-		// Get argument parts
-		let suppliedargs = l.parts();
-		for (name, value) in argnamevec.into_iter().zip(suppliedargs) {
-		    body = body.subst(&name, &value);
-		}
-
-		Ok(body)
+	    // Fixed point recursion
+	    SCons(op, l) if *op == Atom(Fix) => {
+		let ls = match (*l).clone() {
+		    SCons(a, n) if *n == Atom(Nil) => a.clone(),
+		    _ => todo!()
+		}.parts();
+		let argls = ls[1].clone();
+		let argname = match argls {
+		    Atom(Var(name)) => name,
+		    _ => todo!()
+		};
+		let body = ls[4].clone();
+		Ok(body.subst(&argname, &scons(op, l)))
 	    },