fix: step scrutinee of case & can instantiate empty vec

3 files changed, 32 insertions, 0 deletions

diff --git a/src/sexp/case.rs b/src/sexp/case.rs
index d78f7ad..eb98446 100644
--- a/src/sexp/case.rs
+++ b/src/sexp/case.rs
@@ -54,6 +54,7 @@ impl SExp {
      * ```
      */
     pub fn matches_pat(&self, pat: &SExp) -> Option<Vec<(String, SExp)>> {
+	println!("matchin {self} against {pat}");
 	match (self, pat) {
 	    
 	    (a, b) if a == b => Some(vec![]),
diff --git a/src/sexp/step.rs b/src/sexp/step.rs
index 97675fa..bae47a5 100644
--- a/src/sexp/step.rs
+++ b/src/sexp/step.rs
@@ -286,6 +286,20 @@ impl SExp {
     /// );
     /// ```
     ///
+    /// **Pattern matching**
+    /// ```rust
+    /// use myslip::{sexp::{SExp::*, SLeaf::*, util::*}, r#type::{Type::*, util::*}};
+    /// use myslip::parse::parsetree::parse_to_ast;
+    ///
+    /// let exp = "case (+ 1 2) (3 true) (_ false)";
+    /// let exp = parse_to_ast(exp);
+    /// let exp = exp.and_then(|e| e.step());
+    /// let expshould = parse_to_ast("case 3 (3 true) (_ false)");
+    /// assert_eq!(exp, expshould);
+    /// let exp = exp.and_then(|e| e.step());
+    /// assert_eq!(exp, Ok(Atom(True)));
+    /// ```
+    ///
     /// Shadowing:
     /// ```rust
     /// use myslip::sexp::{SExp::*, SLeaf::*, util::*};
@@ -352,6 +366,10 @@ impl SExp {
 	    // case expressions
 	    SCons(op, l) if scons(op.clone(), l.clone()).check_case().is_some() => {
 		let (scrutinee, patarms) = scons(op, l).check_case().unwrap();
+		if !scrutinee.is_value() {
+		    return Ok(SExp::back_to_case(scrutinee.step()?, patarms));
+		//     return scons(Case, scons(scrutinee.step()?))
+		}
 
 		let scrutinee = match scrutinee {
 		    SCons(q, v) if *q == Atom(Quote) || *q == Atom(Vector) => *v,
@@ -627,6 +645,11 @@ impl SExp {
                 }
 	    },
 
+	    // Nil in list
+	    SCons(op, l) if *op == Atom(Nil) => {
+		Ok(scons(Vector, Nil))
+	    },
+
 	    // Print
 	    SCons(op, l) if *op == Atom(Print) => {
 		println!("{}", *l);
diff --git a/src/sexp/util.rs b/src/sexp/util.rs
index 3de45d4..aa7ae18 100644
--- a/src/sexp/util.rs
+++ b/src/sexp/util.rs
@@ -94,4 +94,12 @@ impl SExp {
 	    _ => None,
 	}
     }
+
+    pub fn back_to_case(scrutinee: SExp, arms: Vec<SExp>) -> SExp {
+	let mut res = Atom(Nil);
+	for arm in arms.into_iter().rev() {
+	    res = scons(arm, res);
+	}
+	scons(Case, scons(scrutinee, res))
+    }
 }