Add un and under inverses for &cd (#797)

* Add `un` and `under` inverses for `&cd`

- `°&cd` will output the current directory.
- `⍜&cd` will switch back to the original directory after calling `⍜`'s second function

* Update documentation

Author: Omnikar

changelog.md

@@ -41,6 +41,9 @@ This version is not yet released. If you are reading this on the website, then t
   - [`&udpsml`](https://uiua.org/docs/&udpsml) to set the maximum message length
 - Rename `◿ modulus` to [`modulo ◿`](https://uiua.org/docs/modulo)
   - "Modulo" is the correct term for the operation this function conducts
+- Add [`un °`](https://uiua.org/docs/un) and [`under ⍜`](https://uiua.org/docs/under) capability to [`&cd`](https://uiua.org/docs/&cd)
+  - [`un °`](https://uiua.org/docs/un)[`&cd`](https://uiua.org/docs/&cd) will output the current working directory
+  - [`under ⍜`](https://uiua.org/docs/under)[`&cd`](https://uiua.org/docs/&cd) will return to the original directory afterward
 ### Interpreter
 - The fomatter no longer truncates trailing decimal `0`s from number literals
 - Implement filled adjacent [`stencil ⧈`](https://uiua.org/docs/stencil)

parser/src/defs.rs

@@ -3686,6 +3686,9 @@ sys_op! {
     /// [under][&runs] calls [&cl] on all 3 streams automatically.
     (1(3), RunStream, Command, "&runs", "run command stream", Mutating),
     /// Change the current directory
+    ///
+    /// [un][&cd] will output the current working directory.
+    /// [under][&cd] will return to the original directory afterward.
     (1(0), ChangeDirectory, Filesystem, "&cd", "change directory", Mutating),
     /// Get the contents of the clipboard
     ///

site/src/primitive.rs

@@ -279,6 +279,7 @@ fn all_uns() -> impl IntoView {
             { inverse_row([ImageEncode], Optional, "Decodes bytes", None) }
             { inverse_row([GifEncode], Optional, "Decodes bytes", None) }
             { inverse_row([Sys(Clip)], No, "Set the clipboard", None) }
+            { inverse_row([Sys(ChangeDirectory)], No, "Get the current directory", None) }
             { inverse_row([Sys(RawMode)], No, "Terminal raw state", None) }
         </table>
     }
@@ -359,6 +360,7 @@ fn all_unders() -> impl IntoView {
             { inverse_row([Sys(TcpAccept)], Optional, view!("Calls "<Prim prim=Sys(Close)/>" on handle"), None) }
             { inverse_row([Sys(FReadAllStr)], Optional, view!("Calls "<Prim prim=Sys(FWriteAll)/>), None) }
             { inverse_row([Sys(FReadAllBytes)], Optional, view!("Calls "<Prim prim=Sys(FWriteAll)/>), None) }
+            { inverse_row([Sys(ChangeDirectory)], Optional, "Returns to original directory", None) }
             { inverse_row([Sys(RawMode)], Optional, "Resets raw state", None) }
         </table>
     }

src/compile/invert/un.rs

@@ -1267,6 +1267,7 @@ inverse!(PrimPat, input, _, Prim(prim, span), {
         AudioEncode => ImplPrim(AudioDecode, span),
         ImageEncode => ImplPrim(ImageDecode, span),
         Sys(SysOp::Clip) => ImplPrim(UnClip, span),
+        Sys(SysOp::ChangeDirectory) => ImplPrim(UnChangeDirectory, span),
         Sys(SysOp::RawMode) => ImplPrim(UnRawMode, span),
         Hsv => ImplPrim(UnHsv, span),
         Json => ImplPrim(UnJson, span),

src/compile/invert/under.rs

@@ -239,6 +239,15 @@ static UNDER_PATTERNS: &[&dyn UnderPattern] = &[
     &(Now, (Now, PushUnd(1)), (Now, PopUnd(1), Sub)),
     &MaybeVal(Store1Copy(Sys(SysOp::FOpen), Sys(SysOp::Close))),
     &MaybeVal(Store1Copy(Sys(SysOp::FCreate), Sys(SysOp::Close))),
+    &MaybeVal((
+        Sys(SysOp::ChangeDirectory),
+        (
+            ImplPrimitive::UnChangeDirectory,
+            PushUnd(1),
+            Sys(SysOp::ChangeDirectory),
+        ),
+        (PopUnd(1), Sys(SysOp::ChangeDirectory)),
+    )),
     &MaybeVal(Store1Copy(Sys(SysOp::TcpConnect), Sys(SysOp::Close))),
     &MaybeVal(Store1Copy(Sys(SysOp::TlsConnect), Sys(SysOp::Close))),
     &MaybeVal(Store1Copy(Sys(SysOp::TcpAccept), Sys(SysOp::Close))),

src/impl_prim.rs

@@ -166,6 +166,7 @@ impl_primitive!(
     (1(2), GifDecode),
     (1(3), AudioDecode),
     (0, UnRawMode, Impure),
+    (0, UnChangeDirectory, Impure),
     (1(0), UnClip, Mutating),
     // Unders
     (1, UndoFix),
@@ -358,6 +359,7 @@ impl fmt::Display for ImplPrimitive {
             GifDecode => write!(f, "{Un}{GifEncode}"),
             AudioDecode => write!(f, "{Un}{AudioEncode}"),
             UnRawMode => write!(f, "{Un}{}", Sys(SysOp::RawMode)),
+            UnChangeDirectory => write!(f, "{Un}{}", Sys(SysOp::ChangeDirectory)),
             UnClip => write!(f, "{Un}{}", Sys(SysOp::Clip)),
             UndoUnBits => write!(f, "{Under}{Un}{Bits}"),
             AntiBase => write!(f, "{Anti}{Base}"),

src/run_prim.rs

@@ -718,6 +718,12 @@ impl ImplPrimitive {
                 let raw_mode = env.rt.backend.get_raw_mode().map_err(|e| env.error(e))?;
                 env.push(raw_mode);
             }
+            ImplPrimitive::UnChangeDirectory => {
+                let cur_dir = (env.rt.backend)
+                    .get_current_directory()
+                    .map_err(|e| env.error(e))?;
+                env.push(cur_dir);
+            }
             ImplPrimitive::UnClip => {
                 let contents = env.pop(1)?.as_string(env, "Contents must be a string")?;
                 (env.rt.backend)

src/sys/mod.rs

@@ -484,6 +484,10 @@ pub trait SysBackend: Any + Send + Sync + 'static {
     fn change_directory(&self, path: &str) -> Result<(), String> {
         Err("Changing directories is not supported in this environment".into())
     }
+    /// Get the current directory
+    fn get_current_directory(&self) -> Result<String, String> {
+        Err("Getting the current directory is not supported in this environment".into())
+    }
     /// Capture an image from the webcam
     fn webcam_capture(&self, index: usize) -> Result<WebcamImage, String> {
         Err("Capturing from webcam is not supported in this environment".into())

src/sys/native.rs

@@ -1123,6 +1123,13 @@ impl SysBackend for NativeSys {
     fn change_directory(&self, path: &str) -> Result<(), String> {
         env::set_current_dir(path).map_err(|e| e.to_string())
     }
+    fn get_current_directory(&self) -> Result<String, String> {
+        env::current_dir().map_err(|e| e.to_string()).and_then(|p| {
+            p.into_os_string()
+                .into_string()
+                .map_err(|_| "Path was not valid unicode".into())
+        })
+    }
     #[cfg(feature = "webcam")]
     fn webcam_capture(&self, index: usize) -> Result<crate::WebcamImage, String> {
         let cam_channels = &NATIVE_SYS.cam_channels;