feat: fixed point dynamics

4 files changed, 81 insertions, 26 deletions

diff --git a/TUTORIAL.md b/TUTORIAL.md
index 8e5165d..d7bf266 100644
--- a/TUTORIAL.md
+++ b/TUTORIAL.md
@@ -199,7 +199,7 @@ For basic lists, the `case`-operator can be used.
 It's syntax is:
 ```myslip
 (case [condition]
-    ([pattern 1] [value 1])
+	([pattern 1] [value 1])
 	([pattern 2] [value 2])
 	...)
 ```
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)))
 	    },
 
 
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) =>
diff --git a/src/type/check.rs b/src/type/check.rs
index d118871..170feec 100644
--- a/src/type/check.rs
+++ b/src/type/check.rs
@@ -483,7 +483,7 @@ impl Type {
 
 #[cfg(test)]
 mod tests {
-    use super::{*, TypeError};
+    use super::*;
 
     #[test]
     fn test_failing_infer_generics() {