feat(executor): handle GoTo case of Update

Author: Julius Bierbaum

src/executor.rs

@@ -21,6 +21,8 @@ use crate::{
     heap::Heap,
 };
 
+use self::op_code::OffsetDirection;
+
 pub struct ExecutorFrame {
     frame: Frame,
     pc: ProgramCounter,
@@ -119,6 +121,12 @@ pub fn run(code: &Code, heap: &mut Heap) {
                 };
                 current_pc.next(1).unwrap();
             },
+            Update::GoTo(offset, direction) => {
+                match direction {
+                    OffsetDirection::Forward => current_pc.next(offset).unwrap(),
+                    OffsetDirection::Backward => current_pc.(offset).unwrap(),
+                }
+            }
         }
     }
 }
@@ -168,6 +176,7 @@ the len is {length} but the index is {index}"
 pub enum Update {
     None,
     Return,
+    GoTo(usize, OffsetDirection),
     MethodCall(Rc<Method>),
 }
 

src/executor/program_counter.rs

@@ -12,7 +12,7 @@ pub enum ProgramCounterError {
     #[error("Index {requested_pos} out of {actual_len}")]
     OutOfBoundsError {
         actual_len: usize,
-        requested_pos: usize,
+        requested_pos: isize,
     },
 }
 
@@ -33,14 +33,23 @@ impl ProgramCounter {
         if self.current_op_codes.len() <= self.current_op_code + offset {
             return Err(ProgramCounterError::OutOfBoundsError {
                 actual_len: self.current_op_codes.len(),
-                requested_pos: self.current_op_code + offset,
+                requested_pos: (self.current_op_code + offset) as isize,
             });
         }
         self.current_op_code += offset;
         Ok(())
     }
 
-    // todo: fn previous() might be needed as offset as usize cannot be negative
+    pub fn previous(&mut self, offset: usize) -> Result<(), ProgramCounterError> {
+        if offset > self.current_op_code {
+            return Err(ProgramCounterError::OutOfBoundsError {
+                actual_len: self.current_op_codes.len(),
+                requested_pos: (self.current_op_code as isize) - (offset as isize),
+            });
+        }
+        self.current_op_code -= offset;
+        Ok(())
+    }
 
     /// absolute
     pub fn set(&mut self, position: usize) -> Result<(), ProgramCounterError> {