add log

src/main.rs

@@ -570,6 +570,7 @@ fn simp(
     for i in 0..step_limit {
         expr = expr
             .apply_special_form::<Genslop>()
+            .apply_special_form::<Log>()
             .apply_special_form::<Let>()
             .apply_special_form::<Eq>();
 
@@ -704,6 +705,25 @@ impl SpecialForm<'_> for Genslop {
     }
 }
 
+static LOG: Lazy<Symbol> = Lazy::new(|| TABLE.lock().unwrap().intern("log").unwrap());
+
+#[derive(Debug, Clone)]
+struct Log<'src>(&'src Sexp);
+
+impl<'src> SpecialForm<'src> for Log<'src> {
+    fn from_sexp(sexp: &'src Sexp) -> Option<Self> {
+        match sexp {
+            Sexp::List(xs) if xs.len() == 2 && *xs[0].atom()? == *LOG => Some(Self(&xs[1])),
+            _ => None,
+        }
+    }
+
+    fn eval(self) -> Sexp {
+        eprintln!("LOG: {}", self.0);
+        self.0.clone()
+    }
+}
+
 fn make_rule(sexp: &Sexp) -> Option<Rule> {
     match sexp {
         Sexp::List(xs) => match &xs[..] {