I went to System Preferences to set up the keyboard shortcuts ⌥⇥ and ⌥⇧⇥ for "Shift Right" and "Shift Left", respectively. The new shortcuts appeared in the Edit menu but neither of them work as intended and simply enter a space character instead.
(I'm working on the Finnish keyboard layout but the same thing happens when I switch to US. For my normal layout, the default key combinations for Shift Left/Right are pretty hard to reach, and ⌥⇥ is much more accessible.)
I had a look at this and it is a consequence of the default meaning of the ⌥ key on OS X keyboards. The operating system intercepts keystrokes where only ⌥ (possibly together with ⇧) is used and converts them into alternative characters. For example, ⌥u gives me the ability to write umlauts like ä and ⌥- produces a double length (–) and ⌥⇧- a tripple length (—) dash (aka emdash). That meaning of the ⌥ key seems to take precedence over settings in System Preferences.
If you try binding "Shift Right" and "Shift Left" to ⌥⌘⇥ and ⌥⇧⌘⇥, it works just fine. So, this appears to be an OS X limitation, rather than a problem with Haskell for Mac. (⌥⌘⇥ and ⌥⇧⌘⇥ works quite well on the US keyboard when you use the ⌘ and ⌥ keys to the right of the spacebar. Maybe that is useful on the Finnish keyboard, too.)
I don't fully buy this explanation because the same key bindings configured in System Preferences work just fine in e.g. Xcode.app.
⌥⌘⇥ is a pretty hard key combination to reach, I'm afraid. Thanks for the idea, anyway.
But in Xcode, do you configure the bindings also in System Preferences or in Xcode's own keyboard shortcut config (i.e., in Xcode preferences)? OS X applications can get access to the raw (key) event stream and, given Xcode's elaborate shortcut preference pane, I wouldn't be surprised if it doesn't just use the high-level APIs.
However, Haskell for Mac doesn't try anything like that, but just processes whatever comes down the standard responder chain. (In other words, I am not claiming that it is impossible to intercept these shortcuts. However, configuring them in System Preferences isn't sufficient. Just to make sure that I don't make any incorrect claims, I just ran Haskell for Mac in the debugger and ⌥⇥ does not trigger the menu for which the shortcut is configured —although, it appears in the menu item— instead, HfM just receives a space character via the responder chain.)
I've used System Preferences for configuring those shortcuts for Xcode.
Sorry for my ignorance about the Finnish layout, but on German keyboards, people sometimes use the umlaut keys for Ö and Ä, which are the key below P and the key to the right of that as a substitute for navigation shortcuts that use [ and ] on the US layout. Maybe something like that could help?
Yeah, I guess I'll need to do something like that in the meantime. It's just slightly an inconvenient context switch when used to binding Tab or Alt+Tab for indentation in other text editors.
Just to double check my theory about what's happening, I did try the same thing with the Chocolat editor <https://chocolatapp.com>, which uses the same binding for Shift Left and Shift Right as HfM by default. Binding those to ⌥⇥ and ⌥⇧⇥ has the same result as in HfM.
On the other hand, Apple's TextEdit configures its own use of ⌥⇥ (to add an itemised bullet point).
Hence, I am quite sure that my theory about what's happening is correct. To get at ⌥⇥, HfM would need to reach deeper into the event system.
In any case, your point is well taken. Those special symbols on the right hand side of the keyboard are rather keyboard layout dependent and make for bad shortcuts on some (maybe many) layouts. I don't see any easy way out of this and am unsure what the best solution is at the moment. In any case, this definitely needs to be improved.
Thanks again for the valuable feedback.