Add instruction dumper

A vector of instructions and constants can now be decompiled as text on
the terminal to give an idea of what the VM is doing.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/compile/thunk.rs

@@ -264,8 +264,9 @@ impl Visit for CompileBody<'_> {
                 let attr = global_sym(expr.access.to_string());
                 thunk.push(Inst::SetAttr(attr));
             }
-            LhsExpr::Local(local) => {
-                let local = global_sym(local.to_string());
+            LhsExpr::Local(local_name) => {
+                let sym = global_sym(local_name.to_string());
+                let local = self.compile.lookup_scope_or_create_global(sym);
                 thunk = Inst::Pop(Some(local)).into();
             }
         }
@@ -320,6 +321,7 @@ impl Visit for CompileBody<'_> {
         for arg in expr.args.iter() {
             thunk.push_thunk(self.visit_expr(&arg)?);
         }
+        thunk.push(Inst::Call(expr.args.len()));
         Ok(thunk)
     }
 
@@ -347,13 +349,7 @@ impl Visit for CompileBody<'_> {
         let thunk = match atom {
             Atom::Ident(ident) => {
                 let sym = global_sym(ident.to_string());
-                let local = if let Some(local) = self.compile.lookup_scope(sym) {
-                    local
-                } else {
-                    // create a global that gets looked up instead, since nothing with this name
-                    // has been declared/assigned in this scope
-                    self.compile.create_global(sym)
-                };
+                let local = self.compile.lookup_scope_or_create_global(sym);
                 // get local
                 Inst::PushLocal(local).into()
             }