rishi/scryer-prolog
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

ENHANCED: partial_string/3 no longer creates atoms

Browse Source 
As a consequence, resulting strings are now quickly reclaimed on
backtracking.

This addresses #2912.

Test case:

    :- use_module(library(iso_ext)).
    :- use_module(library(lists)).

    ab(a).
    ab(b).

Sample query:

    ?- length(Ls, 1_000_000),
       maplist(ab, Ls),
       partial_string(Ls, Es0, []),
       Es0 == Ls.
       Ls = "aaaaaaaaaaaaaaaaaaa ...", Es0 = "aaaaaaaaaaaaaaaaaaa ..."
    ;  Ls = "aaaaaaaaaaaaaaaaaaa ...", Es0 = "aaaaaaaaaaaaaaaaaaa ..."
    ;  Ls = "aaaaaaaaaaaaaaaaaaa ...", Es0 = "aaaaaaaaaaaaaaaaaaa ..."
    ;  Ls = "aaaaaaaaaaaaaaaaaaa ...", Es0 = "aaaaaaaaaaaaaaaaaaa ..."
    ;  Ls = "aaaaaaaaaaaaaaaaaaa ...", Es0 = "aaaaaaaaaaaaaaaaaaa ..."
    ;  ... .

running in constant memory.
This commit is contained in:
Markus Triska
2025-04-25 22:16:44 +02:00
committed by Mark Thom
parent e9bb41f0d6
commit d51cbd67e0
2 changed files with 26 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
src/lib/iso_ext.pl
View File

@@ -22,6 +22,7 @@ but they're not part of the ISO Prolog standard at the moment.
copy_term/3]). copy_term/3]).
:- use_module(library(error), [can_be/2, :- use_module(library(error), [can_be/2,
must_be/2,
domain_error/3, domain_error/3,
instantiation_error/1, instantiation_error/1,
type_error/3]). type_error/3]).
@@ -275,17 +276,15 @@ call_with_inference_limit(_, _, R, Bb, B) :-
; nonvar(R) ; nonvar(R)
). ).
%% partial_string(String, L, L0) %% partial_string(String, Ls0, Ls)
% %
% Explicitly construct a partial string "manually". It can be used as an optimized append/3. % Explicitly construct a partial string "manually". It can be used as an optimized append/3.
% It's not recommended to use this predicate in application code. % It's not recommended to use this predicate in application code.
partial_string(String, L, L0) :- partial_string(String, Ls0, Ls) :-
must_be(chars, String),
( String == [] -> ( String == [] ->
L = L0 Ls0 = Ls
; catch(atom_chars(Atom, String), ; '$create_partial_string'(String, Ls0, Ls)
error(E, _),
throw(error(E, partial_string/3))),
'$create_partial_string'(Atom, L, L0)
). ).
%% partial_string(+String) %% partial_string(+String)

38
src/machine/system_calls.rs
View File

@@ -2479,30 +2479,32 @@ impl Machine {
#[inline(always)] #[inline(always)]
pub(crate) fn create_partial_string(&mut self) { pub(crate) fn create_partial_string(&mut self) {
let atom = cell_as_atom!(self.deref_register(1)); let a1 = self.deref_register(1);
if atom == atom!("") { if let Some(str_like) = self.machine_st.value_to_str_like(a1) {
self.machine_st.fail = true; let str = match str_like {
return; AtomOrString::String(string) => string,
} _ => {
unreachable!()
}
};
let pstr_loc_cell = step_or_resource_error!( let pstr_loc_cell =
self.machine_st, step_or_resource_error!(self.machine_st, self.machine_st.heap.allocate_pstr(&str));
self.machine_st.heap.allocate_pstr(&*atom.as_str())
);
let tail_loc = self.machine_st.heap.cell_len(); let tail_loc = self.machine_st.heap.cell_len();
step_or_resource_error!( step_or_resource_error!(
self.machine_st, self.machine_st,
self.machine_st.heap.push_cell(heap_loc_as_cell!(tail_loc)) self.machine_st.heap.push_cell(heap_loc_as_cell!(tail_loc))
); );
unify!(self.machine_st, self.machine_st.registers[2], pstr_loc_cell); unify!(self.machine_st, self.machine_st.registers[2], pstr_loc_cell);
if !self.machine_st.fail { if !self.machine_st.fail {
let tail = self.machine_st.registers[3]; let tail = self.machine_st.registers[3];
unify!(self.machine_st, tail, heap_loc_as_cell!(tail_loc)); unify!(self.machine_st, tail, heap_loc_as_cell!(tail_loc));
}
} }
} }