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backtrack attributed variable bindings after failure (#242)

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This commit is contained in:
Mark Thom
2019-11-29 13:47:22 -04:00
parent 2d719ab6b7
commit 3e49db1a29
7 changed files with 90 additions and 74 deletions
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82
src/prolog/machine/copier.rs
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@@ -58,34 +58,6 @@ impl<T: CopierTarget> CopyTermState<T> {
}
}
fn reinstantiate_var(&mut self, addr: Addr, threshold: usize) {
match addr {
Addr::HeapCell(h) => {
self.target[threshold] = HeapCellValue::Addr(Addr::HeapCell(threshold));
self.target[h] = HeapCellValue::Addr(Addr::HeapCell(threshold));
self.trail
.push((Ref::HeapCell(h), HeapCellValue::Addr(Addr::HeapCell(h))));
}
Addr::StackCell(fr, sc) => {
self.target[threshold] = HeapCellValue::Addr(Addr::HeapCell(threshold));
self.target.stack()[fr][sc] = Addr::HeapCell(threshold);
self.trail.push((
Ref::StackCell(fr, sc),
HeapCellValue::Addr(Addr::StackCell(fr, sc)),
));
}
Addr::AttrVar(h) => {
let redirect_tag = self.attr_var_redirect_tag();
self.target[threshold] = HeapCellValue::Addr(redirect_tag(threshold));
self.target[h] = HeapCellValue::Addr(redirect_tag(threshold));
self.trail
.push((Ref::AttrVar(h), HeapCellValue::Addr(Addr::AttrVar(h))));
}
_ => {}
}
}
fn copied_list(&mut self, addr: usize) -> bool {
if let HeapCellValue::Addr(Addr::Lis(addr)) = self.target[addr].clone() {
if addr >= self.old_h {
@@ -113,22 +85,10 @@ impl<T: CopierTarget> CopyTermState<T> {
let rd = self.target.store(self.target.deref(ra));
match rd.clone() {
Addr::AttrVar(h) if h >= self.old_h => {
let redirect_tag = self.attr_var_redirect_tag();
self.target[threshold] = HeapCellValue::Addr(redirect_tag(h));
}
Addr::HeapCell(h) if h >= self.old_h => {
Addr::AttrVar(h) | Addr::HeapCell(h) if h >= self.old_h => {
self.target[threshold] = HeapCellValue::Addr(rd)
}
Addr::AttrVar(h) => {
if Addr::AttrVar(h) == rd {
self.reinstantiate_var(Addr::AttrVar(h), threshold);
} else {
let redirect_tag = self.attr_var_redirect_tag();
self.target[threshold] = HeapCellValue::Addr(redirect_tag(h));
}
}
ra @ Addr::HeapCell(..) | ra @ Addr::StackCell(..) => {
ra @ Addr::AttrVar(..) | ra @ Addr::HeapCell(_) | ra @ Addr::StackCell(..) => {
if ra == rd {
self.reinstantiate_var(ra, threshold);
} else {
@@ -148,6 +108,38 @@ impl<T: CopierTarget> CopyTermState<T> {
self.scan += 1;
}
fn reinstantiate_var(&mut self, addr: Addr, threshold: usize) {
match addr {
Addr::HeapCell(h) => {
self.target[threshold] = HeapCellValue::Addr(Addr::HeapCell(threshold));
self.target[h] = HeapCellValue::Addr(Addr::HeapCell(threshold));
self.trail.push((
Ref::HeapCell(h),
HeapCellValue::Addr(Addr::HeapCell(h)),
));
}
Addr::StackCell(fr, sc) => {
self.target[threshold] = HeapCellValue::Addr(Addr::HeapCell(threshold));
self.target.stack()[fr][sc] = Addr::HeapCell(threshold);
self.trail.push((
Ref::StackCell(fr, sc),
HeapCellValue::Addr(Addr::StackCell(fr, sc)),
));
}
Addr::AttrVar(h) => {
let redirect_tag = self.attr_var_redirect_tag();
self.target[threshold] = HeapCellValue::Addr(redirect_tag(threshold));
self.target[h] = HeapCellValue::Addr(redirect_tag(threshold));
self.trail.push((
Ref::AttrVar(h),
HeapCellValue::Addr(Addr::AttrVar(h)),
));
}
_ => unreachable!()
}
}
fn copy_var(&mut self, addr: Addr) {
let rd = self.target.store(self.target.deref(addr.clone()));
@@ -168,7 +160,7 @@ impl<T: CopierTarget> CopyTermState<T> {
self.target
.push(HeapCellValue::Addr(redirect_tag(threshold)));
if let Addr::AttrVar(_) = redirect_tag(threshold) {
if let AttrVarPolicy::DeepCopy = self.attr_var_policy {
let list_val = self.target[h + 1].clone();
self.target.push(list_val);
}
@@ -181,7 +173,9 @@ impl<T: CopierTarget> CopyTermState<T> {
self.reinstantiate_var(addr, scan);
self.scan += 1;
}
_ => *self.value_at_scan() = HeapCellValue::Addr(rd),
_ => {
*self.value_at_scan() = HeapCellValue::Addr(rd);
}
}
}