diff --git a/.gitignore b/.gitignore
index 8ee1bf9..d152bc6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 .stack-work
+result
diff --git a/houseman.cabal b/houseman.cabal
index 96eecf5..a8878e4 100644
--- a/houseman.cabal
+++ b/houseman.cabal
@@ -1,6 +1,10 @@
--- This file has been generated from package.yaml by hpack version 0.13.0.
+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.31.2.
 --
 -- see: https://github.com/sol/hpack
+--
+-- hash: 7ad26b607f812778104a29c85ec86aaf6906f8a3bfeb3f56bb60b2ce29509485
 
 name:                houseman
 version:             0.1.0
@@ -12,7 +16,6 @@ license-file:        LICENSE
 maintainer:          Daisuke Fujimura <me@fujmuradaisuke.com>
 category:            Development
 build-type:          Simple
-cabal-version:       >= 1.10
 
 source-repository head
   type: git
@@ -21,22 +24,23 @@ source-repository head
 library
   hs-source-dirs:
       src
-  ghc-options: -Wall -threaded -rtsopts -with-rtsopts=-N
+  ghc-options: -Weverything -Wno-missing-exported-signatures -Wno-missing-import-lists -Wno-missed-specialisations -Wno-all-missed-specialisations -Wno-unsafe -Wno-safe -Wno-missing-local-signatures -Wno-monomorphism-restriction -Wno-missing-export-lists -threaded -rtsopts -with-rtsopts=-N
   build-depends:
-      base >= 4.7 && < 5
+      base
     , bytestring
-    , text
-    , unix
-    , process
-    , trifecta
-    , parsers
-    , time
-    , optparse-generic >= 1.1.0
-    , dotenv
     , directory
-    , streaming-commons
-    , mtl
+    , dotenv
     , io-streams
+    , mtl
+    , optparse-generic
+    , parsers
+    , process
+    , streaming-commons
+    , tagged
+    , text
+    , time
+    , trifecta
+    , unix
   exposed-modules:
       Houseman
       Houseman.Internal
@@ -44,29 +48,34 @@ library
       Houseman.Types
       Procfile.Parse
       Procfile.Types
+  other-modules:
+      Paths_houseman
   default-language: Haskell2010
 
 executable houseman
   main-is: Main.hs
+  other-modules:
+      Paths_houseman
   hs-source-dirs:
       app
-  ghc-options: -Wall -threaded -rtsopts -with-rtsopts=-N
+  ghc-options: -Weverything -Wno-missing-exported-signatures -Wno-missing-import-lists -Wno-missed-specialisations -Wno-all-missed-specialisations -Wno-unsafe -Wno-safe -Wno-missing-local-signatures -Wno-monomorphism-restriction -Wno-missing-export-lists -threaded -rtsopts -with-rtsopts=-N
   build-depends:
-      base >= 4.7 && < 5
+      base
     , bytestring
-    , text
-    , unix
-    , process
-    , trifecta
-    , parsers
-    , time
-    , optparse-generic >= 1.1.0
-    , dotenv
     , directory
-    , streaming-commons
-    , mtl
-    , io-streams
+    , dotenv
     , houseman
+    , io-streams
+    , mtl
+    , optparse-generic
+    , parsers
+    , process
+    , streaming-commons
+    , tagged
+    , text
+    , time
+    , trifecta
+    , unix
   default-language: Haskell2010
 
 test-suite spec
@@ -74,29 +83,30 @@ test-suite spec
   main-is: Spec.hs
   hs-source-dirs:
       test
-    , src
-  ghc-options: -Wall -threaded -rtsopts -with-rtsopts=-N
+      src
+  ghc-options: -Weverything -Wno-missing-exported-signatures -Wno-missing-import-lists -Wno-missed-specialisations -Wno-all-missed-specialisations -Wno-unsafe -Wno-safe -Wno-missing-local-signatures -Wno-monomorphism-restriction -Wno-missing-export-lists -threaded -rtsopts -with-rtsopts=-N
   build-depends:
-      base >= 4.7 && < 5
+      QuickCheck
+    , base
     , bytestring
-    , text
-    , unix
-    , process
-    , trifecta
-    , parsers
-    , time
-    , optparse-generic >= 1.1.0
-    , dotenv
     , directory
-    , streaming-commons
-    , mtl
+    , dotenv
+    , hspec ==2.*
+    , interpolate
     , io-streams
-    , hspec == 2.*
-    , temporary
+    , mockery
+    , mtl
+    , optparse-generic
+    , parsers
+    , process
     , silently
-    , mockery >= 0.3
-    , interpolate
-    , QuickCheck
+    , streaming-commons
+    , tagged
+    , temporary
+    , text
+    , time
+    , trifecta
+    , unix
   other-modules:
       HousemanSpec
       Procfile.ParseSpec
@@ -106,4 +116,5 @@ test-suite spec
       Houseman.Types
       Procfile.Parse
       Procfile.Types
+      Paths_houseman
   default-language: Haskell2010
diff --git a/package.yaml b/package.yaml
index c9d53ae..67a3362 100644
--- a/package.yaml
+++ b/package.yaml
@@ -6,10 +6,29 @@ license: MIT
 github: fujimura/houseman
 category: Development
 
-ghc-options: -Wall -threaded -rtsopts -with-rtsopts=-N
+ghc-options:
+  # For details on warnings: https://downloads.haskell.org/~ghc/master/users-guide/using-warnings.html
+  # This list taken from https://medium.com/mercury-bank/enable-all-the-warnings-a0517bc081c3
+  # Enable all warnings with -Weverything, then disable the ones we don’t care about
+  - -Weverything
+  - -Wno-missing-exported-signatures # missing-exported-signatures turns off the more strict -Wmissing-signatures. See https://ghc.haskell.org/trac/ghc/ticket/14794#ticket
+  - -Wno-missing-import-lists # Requires explicit imports of _every_ function (e.g. ‘$’); too strict
+  - -Wno-missed-specialisations # When GHC can’t specialize a polymorphic function. No big deal and requires fixing underlying libraries to solve.
+  - -Wno-all-missed-specialisations # See missed-specialisations
+  - -Wno-unsafe # Don’t use Safe Haskell warnings
+  - -Wno-safe # Don’t use Safe Haskell warnings
+  - -Wno-missing-local-signatures # Warning for polymorphic local bindings; nothing wrong with those.
+  - -Wno-monomorphism-restriction # Don’t warn if the monomorphism restriction is used
+
+  # TODO: fix these
+  - -Wno-missing-export-lists
+
+  - -threaded
+  - -rtsopts
+  - -with-rtsopts=-N
 
 dependencies:
-  - base >= 4.7 && < 5
+  - base
   - bytestring
   - text
   - unix
@@ -17,12 +36,13 @@ dependencies:
   - trifecta
   - parsers
   - time
-  - optparse-generic >= 1.1.0
+  - optparse-generic
   - dotenv
   - directory
   - streaming-commons
   - mtl
   - io-streams
+  - tagged
 
 library:
   source-dirs: src
@@ -44,6 +64,6 @@ tests:
       - hspec == 2.*
       - temporary
       - silently
-      - mockery >= 0.3
+      - mockery
       - interpolate
       - QuickCheck
diff --git a/stack.yaml b/stack.yaml
index 22c12df..7e5b6cf 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,16 +1,17 @@
 # For more information, see: https://github.com/commercialhaskell/stack/blob/release/doc/yaml_configuration.md
 
 # Specifies the GHC version and set of packages available (e.g., lts-3.5, nightly-2015-09-21, ghc-7.10.2)
-resolver: lts-5.15
+resolver: lts-13.30
 
 # Local packages, usually specified by relative directory name
 packages:
 - '.'
 
 # Packages to be pulled from upstream that are not in the resolver (e.g., acme-missiles-0.3)
-extra-deps:
-  - optparse-generic-1.1.0
-  - dotenv-0.3.0.1
+
+# extra-deps:
+#   - optparse-generic-1.3.0@sha256:9a86164276f1d7eda9f3e3d115093b9e9c969f2a4d3cee93e1c283f300feb3d1
+  # - dotenv-0.3.0.1
 
 # Override default flag values for local packages and extra-deps
 flags: {}
@@ -32,3 +33,7 @@ extra-package-dbs: []
 # Extra directories used by stack for building
 # extra-include-dirs: [/path/to/dir]
 # extra-lib-dirs: [/path/to/dir]
+
+nix:
+  enable: true
+  shell-file: shell.nix
diff --git a/test/fixtures/echo.sh b/test/fixtures/echo.sh
index 626ccd4..69700fb 100755
--- a/test/fixtures/echo.sh
+++ b/test/fixtures/echo.sh
@@ -1,4 +1,4 @@
-#! /bin/bash
+#!/usr/bin/env bash
 
 echo "ECHO=${ECHO}"
 for var in "$@"
diff --git a/test/fixtures/error.sh b/test/fixtures/error.sh
index e6b915e..70d9ca9 100755
--- a/test/fixtures/error.sh
+++ b/test/fixtures/error.sh
@@ -1,4 +1,4 @@
-#! /bin/bash
+#!/usr/bin/env bash
 
 echo 'error' >&2
 echo 'error' >&2