Make the main frame "extendable" allowing us to not have locals until needed

src/frame.rs

@@ -6,6 +6,7 @@ pub struct Frame {
     pub base: usize,
     pub stack: Stack,
     pub locals: Vec<i32>,
+    pub can_extend_locals: bool,
 }
 
 impl Frame {
@@ -17,6 +18,19 @@ impl Frame {
             base,
             stack: Stack::new(),
             locals: vec![0; num_locals],
+            can_extend_locals: false,
+        }
+    }
+
+    pub fn new_extendable(base: usize) -> Frame {
+        if cfg!(feature = "debug:frame") {
+            println!("Initializing extendable frame");
+        }
+        Frame {
+            base,
+            stack: Stack::new(),
+            locals: Vec::new(),
+            can_extend_locals: true,
         }
     }
 
@@ -28,16 +42,24 @@ impl Frame {
         self.locals.is_empty()
     }
 
-    pub fn get(&self, offset: usize) -> Result<i32> {
+    pub fn get(&mut self, offset: usize) -> Result<i32> {
         if offset >= self.locals.len() {
-            return Err("Local variable out of range");
+            if self.can_extend_locals {
+                self.locals.resize(offset + 1, 0);
+            } else {
+                return Err("Local variable out of range");
+            }
         }
         Ok(self.locals[offset])
     }
 
     pub fn set(&mut self, offset: usize, val: i32) -> Result<()> {
         if offset >= self.locals.len() {
-            return Err("Local variable out of range");
+            if self.can_extend_locals {
+                self.locals.resize(offset + 1, 0);
+            } else {
+                return Err("Local variable out of range");
+            }
         }
         self.locals[offset] = val;
         Ok(())

src/machine.rs

@@ -16,7 +16,6 @@ use heap::Heap;
 use netstack::NetStack;
 
 pub const MAGIC_HEADER: u32 = 0x1DEA_DFAD;
-const ANTI_BS_SIZE: usize = 0xFF;
 
 pub struct Machine {
     pub wide: bool,
@@ -41,7 +40,7 @@ impl Machine {
             halted: false,
             pool,
             block,
-            frame: vec![Frame::new(ANTI_BS_SIZE, 0)],
+            frame: vec![Frame::new_extendable(0)],
             stream_in: Box::new(::std::io::stdin()),
             stream_out: Arc::new(Mutex::new(::std::io::stdout())),