From 2768beec4c49660a0636b93e585790efd62dbe6a Mon Sep 17 00:00:00 2001
From: Markus Triska <triska@metalevel.at>
Date: Sun, 19 Jul 2020 11:07:03 +0200
Subject: [PATCH] ADDED: path_segments/2 for portable reasoning about path
 components.

The platform-specific directory separator is taken into account.
The clean representation of segments as a list simplifies reasoning.
---
 src/clause_types.rs         |  3 ++
 src/lib/files.pl            | 55 +++++++++++++++++++++++++++++++++++++
 src/machine/system_calls.rs |  4 +++
 3 files changed, 62 insertions(+)

diff --git a/src/clause_types.rs b/src/clause_types.rs
index f43b30fd..ab555630 100644
--- a/src/clause_types.rs
+++ b/src/clause_types.rs
@@ -175,6 +175,7 @@ pub enum SystemClauseType {
     FileSize,
     FileExists,
     DirectoryExists,
+    DirectorySeparator,
     MakeDirectory,
     DeleteFile,
     WorkingDirectory,
@@ -344,6 +345,7 @@ impl SystemClauseType {
             &SystemClauseType::FileSize => clause_name!("$file_size"),
             &SystemClauseType::FileExists => clause_name!("$file_exists"),
             &SystemClauseType::DirectoryExists => clause_name!("$directory_exists"),
+            &SystemClauseType::DirectorySeparator => clause_name!("$directory_separator"),
             &SystemClauseType::MakeDirectory => clause_name!("$make_directory"),
             &SystemClauseType::DeleteFile => clause_name!("$delete_file"),
             &SystemClauseType::WorkingDirectory => clause_name!("$working_directory"),
@@ -682,6 +684,7 @@ impl SystemClauseType {
             ("$file_size", 2) => Some(SystemClauseType::FileSize),
             ("$file_exists", 1) => Some(SystemClauseType::FileExists),
             ("$directory_exists", 1) => Some(SystemClauseType::DirectoryExists),
+            ("$directory_separator", 1) => Some(SystemClauseType::DirectorySeparator),
             ("$make_directory", 1) => Some(SystemClauseType::MakeDirectory),
             ("$delete_file", 1) => Some(SystemClauseType::DeleteFile),
             ("$working_directory", 2) => Some(SystemClauseType::WorkingDirectory),
diff --git a/src/lib/files.pl b/src/lib/files.pl
index da511d06..bdc38b90 100644
--- a/src/lib/files.pl
+++ b/src/lib/files.pl
@@ -54,6 +54,7 @@
                   make_directory/1,
                   working_directory/2,
                   path_canonical/2,
+                  path_segments/2,
                   file_modification_time/2,
                   file_creation_time/2,
                   file_access_time/2]).
@@ -143,3 +144,57 @@ file_creation_time(File, T) :-
 file_time_(File, Which, T) :-
         '$file_time'(File, Which, T0),
         read_term_from_chars(T0, T).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   path_segments(Ps, Segments): True iff Segments are the segments of Ps.
+
+   Segments is the list of components of the path Ps that are
+   separated by the platform-specific directory separator. Each
+   segment is a list of characters.
+
+   At least one of the arguments must be instantiated.
+
+   Examples:
+
+      ?- path_segments("/hello/there", Segments).
+         Segments = [[],"hello","there"]
+      ;  false.
+
+      ?- path_segments(Path, ["hello","there"]).
+         Path = "hello/there"
+      ;  false.
+
+
+   To obtain the platform-specific directory separator, you can use:
+
+      ?- path_segments(Separator, ["",""]).
+         Separator = "/"
+      ;  false.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+path_segments(Path, Segments) :-
+        '$directory_separator'(Sep),
+        (   var(Path) ->
+            must_be(list, Segments),
+            maplist(list_of_chars, Segments),
+            append_with_separator(Segments, Sep, Path)
+        ;   list_of_chars(Path),
+            path_to_segments(Path, Sep, Segments)
+        ).
+
+append_with_separator([], _, []).
+append_with_separator([Segment|Segments], Sep, Path) :-
+        append_with_separator_(Segments, Segment, Sep, Path).
+
+append_with_separator_([], Segment, _, Segment).
+append_with_separator_([Segment|Segments], Prev, Sep, Path) :-
+        append(Prev, [Sep|Rest], Path),
+        append_with_separator_(Segments, Segment, Sep, Rest).
+
+path_to_segments(Path, Sep, Segments) :-
+        (   append(Front, [Sep|Ps], Path) ->
+            Segments = [Front|Rest],
+            path_to_segments(Ps, Sep, Rest)
+        ;   Segments = [Path]
+        ).
diff --git a/src/machine/system_calls.rs b/src/machine/system_calls.rs
index 3d150107..31024167 100644
--- a/src/machine/system_calls.rs
+++ b/src/machine/system_calls.rs
@@ -870,6 +870,10 @@ impl MachineState {
                     return Ok(());
                 }
             }
+            &SystemClauseType::DirectorySeparator => {
+                let addr = self.heap.put_constant(Constant::Char(std::path::MAIN_SEPARATOR));
+                self.unify(self[temp_v!(1)], addr);
+            }
             &SystemClauseType::MakeDirectory => {
                 let directory = self.heap_pstr_iter(self[temp_v!(1)]).to_string();
 
-- 
2.54.0