From 56ccf2b054816870311a75d19e32db8446f60f6d Mon Sep 17 00:00:00 2001
From: Konstantin Nazarov <mail@knazarov.com>
Date: Mon, 26 Aug 2024 13:36:01 +0100
Subject: [PATCH] Handle empty lines in REPL

---
 src/compiler.cpp | 19 +++++++++++++++++++
 src/vli.cpp      |  4 +++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/compiler.cpp b/src/compiler.cpp
index adff360..f222e1f 100644
--- a/src/compiler.cpp
+++ b/src/compiler.cpp
@@ -158,6 +158,25 @@ Result<bool> is_comparison_op(Symbol& sym) {
 Result<Value> Compiler::compile(Value& expr) {
   auto context = TRY(Context::create());
 
+  // If expression is empty - just return nil
+  if (expr.is<Nil>()) {
+    auto ex = TRY(Expression::create());
+    uint64_t reg = context.alloc_reg();
+    int64_t c = TRY(context.add_const(TRY(Nil::create())));
+    TRY(ex.add_opcode(Oc::Mov, {0, (int64_t)reg}, {1, c}));
+    TRY(ex.add_opcode(Oc::Ret, {0, (int64_t)reg}));
+    ex.reg = reg;
+
+    Value name = TRY(Nil::create());
+    auto fun = TRY(Function::create(name, 0, context.constants, ex.code,
+                                    TRY(Array::create())));
+
+    auto mod = TRY(Module::create(name, fun, context.globals_dict));
+
+    return Value(std::move(mod));
+  }
+
+  // Otherwise perform actual compilation of the expression
   if (!expr.is<Pair>()) {
     return ERROR(CompilationError);
   }
diff --git a/src/vli.cpp b/src/vli.cpp
index 4f35e87..13cfb09 100644
--- a/src/vli.cpp
+++ b/src/vli.cpp
@@ -31,7 +31,9 @@ Result<void> run_repl() {
   while (true) {
     auto src = TRY(read_line("vli> "));
     auto res = TRY(run_string(src));
-    debug_print(res);
+    if (!res.is<Nil>()) {
+      debug_print(res);
+    }
   }
 
   return Result<void>();