add piston nix pkg for ghc-haskell

runtimes/default.nix

@@ -42,4 +42,5 @@ args: {
     "jelly" = import ./jelly.nix args;
     "openjdk-java" = import ./openjdk-java.nix args;
     "iverilog" = import ./iverilog.nix args;
+    "ghc-haskell" = import ./ghc-haskell.nix args;
 }

runtimes/ghc-haskell.nix

@@ -0,0 +1,37 @@
+{pkgs, piston, ...}:
+let
+    pkg = pkgs.haskell.compiler.ghcHEAD;
+in piston.mkRuntime {
+    language = "haskell";
+    version = pkg.version;
+    runtime = "ghc";
+
+    aliases = [
+        "hs"
+    ];
+    
+    compile = ''
+        rename 's/$/\.hs/' "$@" # Add .hs extension
+        ${pkg}/bin/ghc -dynamic -v0 -o out *.hs
+        chmod +x out
+    '';
+
+    run = ''
+        shift # Filename is only used to compile
+        ./out "$@"
+    '';
+
+    tests = [
+        (piston.mkTest {
+            files = {
+                "test.hs" = ''
+                    main = putStrLn "OK"
+                '';
+            };
+            args = [];
+            stdin = "";
+            packages = [];
+            main = "test.hs";
+        })
+    ];
+}