Implement numerical for loops

examples/test.lua

@@ -40,6 +40,6 @@ print(true or 0)
 global value, table = f(10, 11, 12)
 
 print("hello")
-for i=1,10 do
+for i=#table,1,-1 do
     print(table[i])
 end

src/compile.rs

@@ -380,9 +380,7 @@ impl Statement {
                 scope.locals.insert("_END".to_owned(), *end_reg);
                 scope.locals.insert("_STEP".to_owned(), *step_reg);
 
-                let is_eql = scope.register_counter.next();
-                instructions.push(Instruction::LessThan(is_eql, *end_reg, *init_reg));
-                instructions.push(Instruction::Test(scope.register_counter.next(), is_eql, 1));
+                instructions.push(Instruction::ForTest(*init_reg, *end_reg, *step_reg));
 
                 let mut inner_scope = scope.clone();
                 let instr = block.compile(state, &mut inner_scope);
@@ -392,7 +390,7 @@ impl Statement {
                 instructions.extend(instr);
 
                 instructions.push(Instruction::Add(*init_reg, *init_reg, *step_reg));
-                instructions.push(Instruction::Jmp(-(instr_len + 5)));
+                instructions.push(Instruction::Jmp(-(instr_len + 4)));
             }
         }
 

src/vm.rs

@@ -152,6 +152,12 @@ pub enum Instruction {
     Jmp(i32),
     /// if (R(B) <=> C) then R(A) := R(B) else PC++
     Test(u16, u16, u16),
+    /// if R(C) >= 0
+    ///     then if R(A) < R(B)
+    ///         PC ++
+    ///     otherwise if R(A) > R(B)
+    ///         PC ++
+    ForTest(u16, u16, u16),
     /// [func] [params.len()] [ret_regs.len()]
     /// R(A), ... R(A+C-2) := R(A)(R(A+1), ... R(A+B-1))
     Call(u16, u16, u16),
@@ -185,6 +191,9 @@ impl Debug for Instruction {
             Instruction::NewTable(arg0) => write!(f, "NEWTABLE {}", arg0),
             Instruction::Jmp(arg0) => write!(f, "JMP {}", arg0),
             Instruction::Test(arg0, arg1, arg2) => write!(f, "TEST {} {} {}", arg0, arg1, arg2),
+            Instruction::ForTest(arg0, arg1, arg2) => {
+                write!(f, "FORTEST {} {} {}", arg0, arg1, arg2)
+            }
             Instruction::Call(arg0, arg1, arg2) => write!(f, "CALL {} {} {}", arg0, arg1, arg2),
             Instruction::Close(arg0) => write!(f, "CLOSE {}", arg0),
             Instruction::Closure(arg0, arg1) => write!(f, "CLOSURE {} {}", arg0, arg1),
@@ -898,6 +907,27 @@ impl ClosureRunner {
                         self.program_counter += 1;
                     }
                 }
+                Instruction::ForTest(counter_reg, end_reg, step_reg) => {
+                    let step_gte_0 = match self.get_stack(*step_reg) {
+                        StackValue::Value(value) => Value::Integer(LuaInteger(0)).lt(&value),
+                    };
+                    let counter = match self.get_stack(*counter_reg) {
+                        StackValue::Value(value) => value,
+                    };
+                    let end = match self.get_stack(*end_reg) {
+                        StackValue::Value(value) => value,
+                    };
+
+                    if step_gte_0?.is_truthy() {
+                        if !end.lt(&counter)?.is_truthy() {
+                            self.program_counter += 1;
+                        }
+                    } else {
+                        if !counter.lt(&end)?.is_truthy() {
+                            self.program_counter += 1;
+                        }
+                    }
+                }
                 Instruction::Call(func_reg, param_len, ret_len) => {
                     let param_start_func_reg = *func_reg;