Now warns when Erlang isn't found

Author: chyndman

Elixir.iss

@@ -34,7 +34,25 @@ end;
 procedure InitializeWizard();
 begin
   idpAddFile('@@URL', ExpandConstant('{tmp}\Precompiled.zip'));
-  idpDownloadAfter(wpReady);
+  idpDownloadAfter(wpPreparing);
+end;
+
+function PrepareToInstall(var NeedsRestart: Boolean): String;
+var
+  ErrorMsg: String;
+begin
+  if ErlangIsInstalled then begin
+    Result := '';
+  end else begin
+    ErrorMsg := 'Warning: Erlang does not seem to be installed.' + #13#10#13#10 +
+                'In order for Elixir to run, you will need to install Erlang from http://www.erlang.org/ and then add it to your Path environment variable.' + #13#10#13#10 +
+                'Proceed anyway?';
+    if MsgBox(ErrorMsg, mbConfirmation, MB_YESNO or MB_DEFBUTTON2) = IDYES then begin
+      Result := '';
+    end else begin
+      Result := 'Erlang not installed.';
+    end;
+  end;  
 end;
 
 procedure ExtractPrecompiled();

README.md

@@ -3,13 +3,13 @@
 Part of the Elixir on Windows Google Summer of Code 2014 project, this installer sets up [Elixir](http://elixir-lang.org/) on a Windows machine.
 
 Currently, it will:
+* (Suggest that the user) install Erlang first
 * Download the precompiled Elixir package
 * Extract the package to your favorite directory (or mine)
 * Create shortcuts to IEx and the uninstaller
 
 Currently, it won't:
 * Download the LATEST version of Elixir (currently hardcoded to v0.14.1)
-* (Suggest that the user) install Erlang first
 * Append the user's Path variable
 
 ## Acknowledgements