Attempted pattern matching ternary

[bbrk24]

undo := => engine = Engine.fromJSON json if json? := history.pop()

const undo = () =>(const json? = history.pop()? engine = Engine.fromJSON(json):void 0)

Workaround: put the function body on the next line

undo := =>
  engine = Engine.fromJSON json if json? := history.pop()

[edemaine]

A workaround for now:

undo := =>
  engine = Engine.fromJSON json if json? := history.pop()

So this is probably specific to the "don't wrap fat arrow in braces if it's a one-line expression" rule.