Initial project setup

Partly ported from actions/setup-ruby

src/setup-haskell.ts

@@ -0,0 +1,15 @@
+import * as core from '@actions/core';
+import {findHaskellGHCVersion, cacheHaskellTool} from './installer';
+
+async function run() {
+  try {
+    await cacheHaskellTool('/opt', 'ghc');
+    await cacheHaskellTool('/opt', 'cabal');
+    let ghcVersion = core.getInput('ghc-version');
+    await findHaskellGHCVersion(ghcVersion);
+  } catch (error) {
+    core.setFailed(error.message);
+  }
+}
+
+run();