adopt Mario's solution for the paths

Aegis/Commands.lean

@@ -110,27 +110,14 @@ def sierraLoadString (s : String) : CommandElabM Unit := do
 
 elab "aegis_load_string " s:str : command => sierraLoadString s.getString
 
-elab "aegis_set_path " s:str : command => do
-  let fp : System.FilePath := ⟨s.getString⟩
-  unless ← fp.pathExists do throwError "Could not find cairo directory"
-  modifyEnv (cairoPath.addEntry · fp)
-
-elab "aegis_load_file " s:str : command => do
-  let filePath : System.FilePath := ⟨s.getString⟩
-  let filePath ← toCallerRelativeFilePath filePath
-  match filePath.extension with
-  | .some "sierra" => sierraLoadString <| ← IO.FS.readFile filePath
-  | .some "cairo" =>
-    let filePath ← IO.FS.realPath filePath
-    let args : IO.Process.SpawnArgs :=
-      { cmd := "cairo-compile"
-        args := #["--replace-ids", filePath.toString] }
-    let child ← IO.Process.output args
-    dbg_trace "Compilation stderr: {child.stderr}"
-    dbg_trace "Compilation stdout: {child.stdout}"
-    sierraLoadString child.stdout
-  | _ => throwError "Wrong file extension, must be .cairo or .sierra!"
-
+elab "aegis_load_file " path:term : command => do
+  let str ← Elab.Command.liftTermElabM do
+    let path ← unsafe Elab.Term.evalTerm System.FilePath (.const ``System.FilePath []) path
+    let srcPath := System.FilePath.mk (← readThe Core.Context).fileName
+    let some srcDir := srcPath.parent
+      | throwError "cannot compute parent directory of '{srcPath}'"
+    IO.FS.readFile (srcDir / path)
+  sierraLoadString str
 
 elab "aegis_info" name:str : command => do  -- TODO change from `str` to `ident`
   let env ← getEnv