In @sam.zhou case there is not much ambiguity in the first place. However one of the problem is if the actual parameter provided as complex expression. This is the same problem as with infix function.
The more complex problem I don’t want to have is when function takes multiple parameters.
Also original request was to make parentheses optional. This is not a case with infix function and suggestion by @sam.zhou sounds like to follow the same pattern: if developer provided modifier prefix then no parentheses allowed, otherwise they are required.