There were Typed Inform:
There’s also a language server for Inform 6, although last time I checked there were some bugs.
I suppose it would be possible to add non-obtrusive type annotations with special comments, like JSDoc, but it will have to be well thought out, as said above. Something like:
!! @type Number
Global score = 0;
I’m also currently writing an Inform 6 grammar to enable syntax highlighting in Borogove, because that’s what CodeMirror, the code editor it uses, wants. (No error checking, only highlighting) And it’s a pain: Inform 6’s syntax is ambiguous at place and it allows naming variables like keywords, amongst others. So my grammar will sometimes be approximate, as long the highlighting it gives is correct.
I believe Inform 6 works better with a hand-written parser than a grammar/syntax definition, but I might be wrong.