refactor: import custom error to ast_to_ir, raise unparallelizable er…

…r in pash_compiler

compiler/ast_to_ir.py

@@ -8,6 +8,8 @@
 from util import *
 from parse import from_ast_objects_to_shell
 
+from custom_error import *
+
 ## TODO: Separate the ir stuff to the bare minimum and
 ##       try to move this to the shell_ast folder.
 

compiler/pash_compiler.py

@@ -149,7 +149,7 @@ def compile_optimize_output_script(
 
         ret = optimized_ast_or_ir
     else:
-        raise Exception("Script failed to compile!")
+        raise UnparallelizableError("Script failed to compile!")
 
     return ret