add error handling appartus

src/prolog/machine/machine_errors.rs

@@ -0,0 +1,58 @@
+use prolog::ast::*;
+use prolog::builtins::*;
+use prolog::machine::machine_state::*;
+use prolog::num::bigint::BigInt;
+
+use std::rc::Rc;
+
+pub(super) type MachineError = Vec<HeapCellValue>;
+
+impl MachineState {
+    pub(super) fn evaluation_error(&self, eval_error: EvalError) -> MachineError {
+        functor!("evaluation_error", 1, [heap_atom!(eval_error.as_str())])
+    }
+    
+    pub(super) fn type_error(&self, valid_type: ValidType, culprit: Addr) -> MachineError {
+        functor!("type_error", 2, [heap_atom!(valid_type.as_str()), HeapCellValue::Addr(culprit)])
+    }
+
+    pub(super) fn existence_error(&self, name: ClauseName, arity: usize) -> MachineError {
+        let name = HeapCellValue::Addr(Addr::Con(Constant::Atom(name)));
+        let h = self.heap.h;
+        
+        let mut error = functor!("existence_error", 2, [heap_atom!("procedure"), heap_str!(3 + h)]);
+        error.append(&mut functor!("/", 2, [name, heap_integer!(arity)], Fixity::In));
+        
+        error
+    }
+
+    pub(super) fn instantiation_error(&self) -> MachineError {
+        functor!("instantiation_error")
+    }
+
+    pub(super) fn representation_error(&self, flag: RepFlag) -> MachineError {
+        functor!("representation_error", 1, [heap_atom!(flag.as_str())])
+    }
+
+    pub(super) fn error_form(&self, mut err: MachineError) -> MachineError {
+        let h = self.heap.h;
+        let mut error_form = functor!("error", 2,
+                                      [HeapCellValue::Addr(Addr::HeapCell(h + 3)),
+                                       HeapCellValue::Addr(Addr::HeapCell(h + 2))]);
+        
+        error_form.append(&mut err);
+        error_form
+    }
+    
+    pub(super) fn throw_exception(&mut self, err: MachineError) {
+        let h = self.heap.h;
+
+        self.ball.0 = 0;
+        self.ball.1.truncate(0);
+
+        self.heap.append(err);
+
+        self.registers[1] = Addr::HeapCell(h);        
+        self.goto_throw();
+    }    
+}