writeFennel is writeFennelScript with knobs on

The second parameter is now an options attrset, wherein we will pile
all kinds of cool stuff.

Right now the only cool bit is `mainFunction`, which allows you to
compile a fennel module into a lua script and name the function that
should be executed when the script runs. This makes it easier to
write testable Fennel code, because the test script can require the
module and call stuff in it.

pkgs/default.nix

@@ -52,6 +52,7 @@ in {
     };
   };
   writeFennelScript = callPackage ./write-fennel-script {};
+  writeFennel = callPackage ./write-fennel {};
   writeAshScript = callPackage ./write-ash-script {};
   systemconfig = callPackage ./systemconfig {};
   s6-init-bin =  callPackage ./s6-init-bin {};

pkgs/write-fennel-script/default.nix

@@ -2,30 +2,8 @@
   lua
 , lib
 , fennel
+, writeFennel
 , stdenv
 }:
 name : packages : source :
-  let
-    luapath = builtins.map
-      (f:
-        "${f}/share/lua/${lua.luaversion}/?.lua;" +
-        "${f}/share/lua/${lua.luaversion}/?/init.lua;")
-      packages;
-    luacpath = builtins.map (f: "${f}/lib/lua/${lua.luaversion}/?.so;") packages;
-  in stdenv.mkDerivation {
-    inherit name;
-    src = ./.;
-    nativeBuildInputs = [ fennel ];
-    buildPhase = ''
-      (
-       echo "#!${lua}/bin/lua"
-       echo "package.path = ${lib.strings.escapeShellArg (builtins.concatStringsSep "" luapath)} .. package.path"
-       echo "package.cpath = ${lib.strings.escapeShellArg (builtins.concatStringsSep "" luacpath)} .. package.cpath"
-       fennel --correlate --compile ${source}
-      ) >  ${name}.lua
-    '';
-    installPhase = ''
-      cp ${name}.lua $out
-      chmod +x $out
-    '';
-  }
+writeFennel name { inherit packages; } source

pkgs/write-fennel/default.nix

@@ -0,0 +1,37 @@
+{
+  lua
+, lib
+, fennel
+, stdenv
+}:
+name :
+{
+  packages ? [],
+  correlate ? false,
+  mainFunction ? null
+} @ options : source :
+  let
+    luapath = builtins.map
+      (f:
+        "${f}/share/lua/${lua.luaversion}/?.lua;" +
+        "${f}/share/lua/${lua.luaversion}/?/init.lua;")
+      packages;
+    luacpath = builtins.map (f: "${f}/lib/lua/${lua.luaversion}/?.so;") packages;
+    luaFlags = lib.optionalString (mainFunction !=null) "-e dofile(arg[0]).${mainFunction}()";
+  in stdenv.mkDerivation {
+    inherit name;
+    src = ./.;
+    nativeBuildInputs = [ fennel ];
+    buildPhase = ''
+      (
+       echo "#!${lua}/bin/lua ${luaFlags}"
+       echo "package.path = ${lib.strings.escapeShellArg (builtins.concatStringsSep "" luapath)} .. package.path"
+       echo "package.cpath = ${lib.strings.escapeShellArg (builtins.concatStringsSep "" luacpath)} .. package.cpath"
+       fennel ${if correlate then "--correlate" else ""} --compile ${source}
+      ) >  ${name}.lua
+    '';
+    installPhase = ''
+      cp ${name}.lua $out
+      chmod +x $out
+    '';
+  }