Allow redefining local variables with "fn"

src/compiler.cpp

@@ -820,16 +820,42 @@ Result<Expression> Compiler::compile_fn(Context& context, Symbol& op,
       Oc::MakeClosure, {0, (int64_t)reg},
       {0, (int64_t)reg + (int64_t)TRY(ctx.closures.size()) + 1}));
 
-  if (context.toplevel && !name.is<Nil>()) {
+  if (!name.is<Nil>()) {
+    if (context.toplevel) {
       int64_t gname = TRY(context.add_const(name));
       TRY(ex_res.add_opcode(Oc::GlobalStore, {1, (int64_t)gname},
                             {0, (int64_t)reg}));
-  }
-
       context.maxreg = reg + 1;
       ex_res.reg = reg;
 
       return ex_res;
+    } else {
+      auto maybe_binding = context.get_var(name);
+
+      if (maybe_binding.has_value()) {
+        auto breg = maybe_binding.value();
+        TRY(ex_res.add_opcode(Oc::Mov, {0, (int64_t)breg}, {0, (int64_t)reg}));
+        ex_res.reg = reg;
+
+        context.maxreg = reg + 1;
+        return std::move(ex_res);
+      } else {
+        context.maxreg = reg + 1;
+        auto breg = TRY(context.add_var(name));
+
+        TRY(ex_res.add_opcode(Oc::Mov, {0, (int64_t)breg}, {0, (int64_t)reg}));
+        ex_res.reg = breg;
+        context.maxreg = breg + 1;
+
+        return std::move(ex_res);
+      }
+    }
+  } else {
+    context.maxreg = reg + 1;
+    ex_res.reg = reg;
+
+    return ex_res;
+  }
 }
 
 Result<Expression> Compiler::compile_let(Context& context, Symbol& op,
@@ -924,6 +950,7 @@ Result<Expression> Compiler::compile_body(Context& context, const Value& expr) {
     if (cur.is<Nil>()) {
       ex_res.reg = expr.reg;
     } else {
+      // TODO: commenting this out means we waste registers
       // context.maxreg = maxreg;
     }
   }

test/function.vli

@@ -65,3 +65,13 @@
     (+ x y))
 
 (assert (= (def-redef) 6))
+
+;; allow redefenition of variables with "fn"
+
+(fn def-redef-fn ()
+    (def x 2)
+    (fn x (y) (+ x y))
+    (x 3)
+    )
+
+(assert (= (def-redef-fn) 5))