[#1] Implement core library idea (#2)

Resolves #1

.travis.yml

@@ -4,7 +4,7 @@ language: haskell
 git:
   depth: 5
 
-cabal: "2.0"
+cabal: "2.4"
 
 cache:
   directories:
@@ -17,13 +17,7 @@ matrix:
   - ghc: 8.2.2
   - ghc: 8.4.4
   - ghc: 8.6.3
-  
-  - ghc: 8.2.2
-    env: STACK_YAML="$TRAVIS_BUILD_DIR/stack-8.2.2.yaml"
-  
-  - ghc: 8.4.4
-    env: STACK_YAML="$TRAVIS_BUILD_DIR/stack-8.4.4.yaml"
-  
+
   - ghc: 8.6.3
     env: STACK_YAML="$TRAVIS_BUILD_DIR/stack.yaml"
 

shellmet.cabal

@@ -2,7 +2,7 @@ cabal-version:       2.0
 name:                shellmet
 version:             0.0.0
 synopsis:            Out of the shell solution for scripting in Haskell
-description:         Out of the shell solution for scripting in Haskell
+description:         Shellmet provides easy and convenient way to call shell commands from Haskell programs
 homepage:            https://github.com/kowainik/shellmet
 bug-reports:         https://github.com/kowainik/shellmet/issues
 license:             MPL-2.0
@@ -14,7 +14,9 @@ category:            Shell, Command Line
 build-type:          Simple
 extra-doc-files:     README.md
                    , CHANGELOG.md
-tested-with:         GHC == 8.2.2, GHC == 8.4.4, GHC == 8.6.3
+tested-with:         GHC == 8.2.2
+                     GHC == 8.4.4
+                     GHC == 8.6.3
 
 source-repository head
   type:                git
@@ -23,10 +25,10 @@ source-repository head
 library
   hs-source-dirs:      src
   exposed-modules:     Shellmet
-                       
 
   build-depends:       base >= 4.10.1.0 && < 4.13
-                     
+                     , process ^>= 1.6.3
+                     , text ^>= 1.2.3
 
   ghc-options:         -Wall
                        -Wincomplete-uni-patterns
@@ -58,7 +60,7 @@ test-suite shellmet-test
 
   build-depends:       base >= 4.10.1.0 && < 4.13
                      , shellmet
-                     
+
 
   ghc-options:         -Wall
                        -threaded

src/Shellmet.hs

@@ -1,6 +1,66 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE TypeFamilies      #-}
+
+{- | This module contains neat utilities to be able to work with
+shell commands in generic and simple way using just strings.
+-}
+
 module Shellmet
-       ( someFunc
+       ( ($|)
+       , ($?)
        ) where
 
-someFunc :: IO ()
-someFunc = putStrLn ("someFunc" :: String)
+import Control.Exception (catch)
+import Data.String (IsString (..))
+import Data.Text (Text)
+import System.Process (callCommand, readProcess, showCommandForUser)
+
+import qualified Data.Text as T
+
+
+{- | This instance is needed to provide functionality to call commands by using
+simple string literals in 'IO' monad.
+
+>>> "ls" ["-1"]
+⚙  ls -1
+CHANGELOG.md
+CONTRIBUTING.md
+dist-newstyle
+LICENSE
+README.md
+shellmet.cabal
+src
+stack.yaml
+test
+-}
+instance (a ~ [Text], b ~ IO ()) => IsString (a -> b) where
+    fromString :: String -> [Text] -> IO ()
+    fromString cmd args = do
+        let cmdStr = showCommandForUser cmd (map T.unpack args)
+        putStrLn $ "⚙  " ++ cmdStr
+        callCommand cmdStr
+
+{- | Run shell command with given options and return stripped stdout of the
+executed command.
+
+>>> "echo" $| ["Foo", "Bar"]
+"Foo Bar"
+-}
+infix 5 $|
+($|) :: FilePath -> [Text] -> IO Text
+cmd $| args = T.strip . T.pack <$> readProcess cmd (map T.unpack args) ""
+
+{- | Do some IO actions when processed failed with error.
+
+>>> "exit" ["0"] $? putStrLn "Command failed"
+⚙  exit 0
+
+>>> "exit" ["1"] $? putStrLn "Command failed"
+⚙  exit 1
+Command failed
+-}
+infixl 4 $?
+($?) :: IO () -> IO () -> IO ()
+action $? handler = action `catch` \(_ :: IOError) -> handler

stack-8.2.2.yaml

@@ -1,4 +0,0 @@
-resolver: lts-11.22
-
-ghc-options:
-  "$locals": -fhide-source-paths

stack-8.4.4.yaml

@@ -1,4 +0,0 @@
-resolver: lts-12.25
-
-ghc-options:
-  "$locals": -fhide-source-paths