ADDED: working_directory/2, addressing a remaining aspect of #511

src/clause_types.rs

@@ -177,6 +177,7 @@ pub enum SystemClauseType {
     DirectoryExists,
     MakeDirectory,
     DeleteFile,
+    WorkingDirectory,
     DeleteAttribute,
     DeleteHeadAttribute,
     DynamicModuleResolution(usize),
@@ -343,6 +344,7 @@ impl SystemClauseType {
             &SystemClauseType::DirectoryExists => clause_name!("$directory_exists"),
             &SystemClauseType::MakeDirectory => clause_name!("$make_directory"),
             &SystemClauseType::DeleteFile => clause_name!("$delete_file"),
+            &SystemClauseType::WorkingDirectory => clause_name!("$working_directory"),
             &SystemClauseType::REPL(REPLCodePtr::CompileBatch) => clause_name!("$compile_batch"),
             &SystemClauseType::REPL(REPLCodePtr::UseModule) => clause_name!("$use_module"),
             &SystemClauseType::REPL(REPLCodePtr::UseQualifiedModule) => {
@@ -678,6 +680,7 @@ impl SystemClauseType {
             ("$directory_exists", 1) => Some(SystemClauseType::DirectoryExists),
             ("$make_directory", 1) => Some(SystemClauseType::MakeDirectory),
             ("$delete_file", 1) => Some(SystemClauseType::DeleteFile),
+            ("$working_directory", 2) => Some(SystemClauseType::WorkingDirectory),
             ("$use_module", 1) => Some(SystemClauseType::REPL(REPLCodePtr::UseModule)),
             ("$use_module_from_file", 1) =>
                     Some(SystemClauseType::REPL(REPLCodePtr::UseModuleFromFile)),

src/lib/files.pl

@@ -51,7 +51,8 @@
                   file_exists/1,
                   directory_exists/1,
                   delete_file/1,
-                  make_directory/1]).
+                  make_directory/1,
+                  working_directory/2]).
 
 :- use_module(library(error)).
 :- use_module(library(lists)).
@@ -85,3 +86,8 @@ make_directory(Directory) :-
 delete_file(File) :-
         list_of_chars(File),
         '$delete_file'(File).
+
+working_directory(Dir0, Dir) :-
+        can_be(list, Dir0),
+        can_be(list, Dir),
+        '$working_directory'(Dir0, Dir).

src/machine/system_calls.rs

@@ -890,6 +890,34 @@ impl MachineState {
                     }
                 }
             }
+            &SystemClauseType::WorkingDirectory => {
+                if let Ok(dir) = env::current_dir() {
+                    let current =
+                        match dir.to_str() {
+                            Some(d) => { d }
+                            _ => { let stub = MachineError::functor_stub(clause_name!("working_directory"), 2);
+                                   let err = MachineError::representation_error(RepFlag::Character);
+                                   let err = self.error_form(err, stub);
+
+                                   return Err(err);
+                            }
+                        };
+                    let chars = self.heap.put_complete_string(current);
+                    self.unify(self[temp_v!(1)], chars);
+
+                    let next = self.heap_pstr_iter(self[temp_v!(2)]).to_string();
+
+                    match env::set_current_dir(std::path::Path::new(&next)) {
+                        Ok(_) => { }
+                        _ => { self.fail = true;
+                               return Ok(());
+                        }
+                    }
+                } else {
+                    self.fail = true;
+                    return Ok(());
+                }
+            }
             &SystemClauseType::AtEndOfExpansion => {
                 if self.cp == LocalCodePtr::TopLevel(0, 0) {
                     self.at_end_of_expansion = true;