add file seek (&sb) (#718)

* add file seek (&sb)

* add &sb to primitives.json

* fmt

* allow &sb to seek from file end

* oops

* change seek name to `&seek`

---------

Co-authored-by: Kai Schmidt <[email protected]>

Author: alex-s168

parser/src/defs.rs

@@ -3742,6 +3742,8 @@ sys_op! {
     /// ex: &cl &w "Hello, world!" . &fc "file.txt"
     ///   : &fras "file.txt"
     (2(0), Write, Stream, "&w", "write", Mutating),
+    /// Moves to a absolute position in the file under the stream.
+    (2(0), Seek, Stream, "&seek", "seek", Mutating),
     /// Invoke a path with the system's default program
     (1(1), Invoke, Command, "&invk", "invoke", Mutating),
     /// Close a stream by its handle

site/primitives.json

@@ -335,6 +335,12 @@
     "class": "Stream",
     "description": "Write an array to a stream"
   },
+  "&sb": {
+    "args": 2,
+    "outputs": 0,
+    "class": "Stream",
+    "description": "Goes to the position in a stream"
+  },
   "above": {
     "glyph": "◠",
     "outputs": 1,
@@ -1475,4 +1481,4 @@
     "class": "Encoding",
     "description": "Encode an array into XLSX bytes"
   }
-}
+}

src/sys/mod.rs

@@ -298,6 +298,10 @@ pub trait SysBackend: Any + Send + Sync + 'static {
     fn write(&self, handle: Handle, contents: &[u8]) -> Result<(), String> {
         Err("Writing to streams is not supported in this environment".into())
     }
+    /// Go to an absolute file position
+    fn seek(&self, handle: Handle, offset: std::io::SeekFrom) -> Result<(), String> {
+        Err("Seeking streams is not supported in this environment".into())
+    }
     /// Create a file
     fn create_file(&self, path: &Path) -> Result<Handle, String> {
         Err("Creating files is not supported in this environment".into())
@@ -860,6 +864,17 @@ pub(crate) fn run_sys_op(op: &SysOp, env: &mut Uiua) -> UiuaResult {
                 _ => (env.rt.backend.write(handle, &bytes)).map_err(|e| env.error(e))?,
             }
         }
+        SysOp::Seek => {
+            use std::io::SeekFrom;
+
+            let pos = env.pop(1)?.as_int(env, None)?;
+            let pos = match pos {
+                ..0 => SeekFrom::End(pos as i64),
+                0.. => SeekFrom::Start(pos as u64),
+            };
+            let handle = env.pop(2)?.as_handle(env, None)?;
+            env.rt.backend.seek(handle, pos).map_err(|e| env.error(e))?;
+        }
         SysOp::FReadAllStr => {
             let path = env.pop(1)?.as_string(env, "Path must be a string")?;
             let bytes = (env.rt.backend)

src/sys/native.rs

@@ -608,6 +608,14 @@ impl SysBackend for NativeSys {
             }
         }
     }
+    fn seek(&self, handle: Handle, offset: std::io::SeekFrom) -> Result<(), String> {
+        use std::io::Seek;
+
+        match NATIVE_SYS.get_stream(handle)? {
+            SysStream::File(mut file) => file.seek(offset).map_err(|e| e.to_string()).map(|_| ()),
+            _ => Err("Cannot seek this stream".into()),
+        }
+    }
     #[cfg(feature = "clipboard")]
     fn clipboard(&self) -> Result<String, String> {
         use arboard::*;