assembler: add while_loop

src/assembler.rs

@@ -42,8 +42,26 @@ impl Assembler {
         self
     }
 
+    pub fn while_loop(mut self, mut condition: Assembler, mut body: Assembler) -> Assembler {
+        let cond_len = condition.instructions.len();
+        let body_len = body.instructions.len();
+        self.instructions.append( &mut condition.instructions );
+
+        // jump to end
+        self.instructions.push( VM_Instruction::Branch as VM_Word );
+        self.instructions.push( body_len as VM_Word + 2 );
+
+        self.instructions.append( &mut body.instructions );
+
+        // jump back to condition
+        self.instructions.push( VM_Instruction::Jmp as VM_Word );
+        self.instructions.push( -2-(body_len as VM_Word)-2-(cond_len as VM_Word) ); 
+
+        self
+    }
+
     pub fn branch(mut self, mut if_branch: Assembler, mut else_branch: Assembler) -> Assembler {
-        self.instructions.push(VM_Instruction::Branch as VM_Word );
+        self.instructions.push(VM_Instruction::Branch as VM_Word);
         self.instructions.push( if_branch.instructions.len() as VM_Word + 2);
 
         self.instructions.append( &mut if_branch.instructions );

src/vm.rs

@@ -4,7 +4,7 @@ pub type VM_Word = i64;
 #[repr(u64)]
 pub enum VM_Instruction {
     Nop, Jmp, Call, Branch, Ret,
-    Lit, Dup, Drop, Swap, Rot,
+    Lit, Pick, Roll, Dup, Drop, Swap, Rot,
     Fetch, Store,
     Accept, Emit,
     Add, //Sub, Mul, Div, Rem,
@@ -103,6 +103,23 @@ impl VM {
                 let val = char::from(self.data_stack.pop().expect("emit expects value") as u8);
                 print!("{}", val);
             }
+            VM_Instruction::Pick => {
+                let n = self.data_stack.pop().expect("pick requires index") as usize;
+                self.data_stack.push( *self.data_stack.get( self.data_stack.len() - n ).expect("pick invalid index") );
+            }
+            VM_Instruction::Roll => {
+                let n = self.data_stack.pop().expect("pick requires index") as usize;
+                let l = self.data_stack.len();
+                if n <= l {
+                    if n > 1 {
+                        let val = self.data_stack.remove( l-n );
+                        self.data_stack.push( val );
+                    }
+                } else {
+                    eprintln!("stack = {:?}", self.data_stack);
+                    eprintln!("roll invalid index");
+                }
+            }
             VM_Instruction::Dup => {
                 self.data_stack.push( *self.data_stack.last().expect("dup expect val") );
             }