Curious use of .assuming in S06

[Autrijus Tang]

In S06's Currying section, there are some strange looking examples:

    &textfrom := &substr.assuming(:str($text) :len(Inf));

    &textfrom := &substr.assuming:str($text):len(Inf);

    &woof ::= &bark:(Dog).assuming :pitch<low>;

Why is it allowed to omit comma between adverbial pairs, and even
omit parens around method call arguments?  Is .assuming a special form?

This is S06-specific; neither A06 nor E06 exhibits this syntax.

Thanks,
/Autrijus/

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