diff --git a/src/Pure/Tools/ghc.ML b/src/Pure/Tools/ghc.ML
--- a/src/Pure/Tools/ghc.ML
+++ b/src/Pure/Tools/ghc.ML
@@ -1,92 +1,92 @@
 (*  Title:      Pure/Tools/ghc.ML
     Author:     Makarius
 
 Support for GHC: Glasgow Haskell Compiler.
 *)
 
 signature GHC =
 sig
   val print_codepoint: UTF8.codepoint -> string
   val print_symbol: Symbol.symbol -> string
   val print_string: string -> string
   val project_template: {depends: string list, modules: string list} -> string
   val new_project: Path.T -> {name: string, depends: string list, modules: string list} -> unit
 end;
 
 structure GHC: GHC =
 struct
 
 (** string literals **)
 
 fun print_codepoint c =
   (case c of
     34 => "\\\""
   | 39 => "\\'"
   | 92 => "\\\\"
   | 7 => "\\a"
   | 8 => "\\b"
   | 9 => "\\t"
   | 10 => "\\n"
   | 11 => "\\v"
   | 12 => "\\f"
   | 13 => "\\r"
   | c =>
       if c >= 32 andalso c < 127 then chr c
       else "\\" ^ string_of_int c ^ "\\&");
 
 fun print_symbol sym =
   (case Symbol.decode sym of
     Symbol.Char s => print_codepoint (ord s)
   | Symbol.UTF8 s => UTF8.decode_permissive s |> map print_codepoint |> implode
   | Symbol.Sym s => "\\092<" ^ s ^ ">"
   | Symbol.Control s => "\\092<^" ^ s ^ ">"
   | _ => translate_string (print_codepoint o ord) sym);
 
 val print_string = quote o implode o map print_symbol o Symbol.explode;
 
 
 
 (** project setup **)
 
 fun project_template {depends, modules} =
   \<^verbatim>\<open>{-# START_FILE {{name}}.cabal #-}
 name:                {{name}}
 version:             0.1.0.0
 homepage:            default
 license:             BSD3
 author:              default
 maintainer:          default
 category:            default
 build-type:          Simple
 cabal-version:       >=1.10
 
 executable {{name}}
   hs-source-dirs:      src
   main-is:             Main.hs
   default-language:    Haskell2010
   build-depends:       \<close> ^ commas ("base >= 4.7 && < 5" :: depends) ^
   \<^verbatim>\<open>
   other-modules:       \<close> ^ commas modules ^
   \<^verbatim>\<open>
 {-# START_FILE Setup.hs #-}
 import Distribution.Simple
 main = defaultMain
 
 {-# START_FILE src/Main.hs #-}
 module Main where
 
 main :: IO ()
 main = return ()
 \<close>;
 
 fun new_project dir {name, depends, modules} =
   let
     val template_path = dir + (Path.basic name |> Path.ext "hsfiles");
     val _ = File.write template_path (project_template {depends = depends, modules = modules});
-    val {rc, err, ...} =
-      Isabelle_System.bash_process
+    val _ =
+      Isabelle_System.bash_output_check
         ("cd " ^ File.bash_path dir ^ "; isabelle ghc_stack new " ^ Bash.string name ^
           " --bare " ^ File.bash_platform_path template_path);
-  in if rc = 0 then () else error err end;
+  in () end;
 
 end;