I wonder why a keyword should be limited to a symbol (or special
symbol)?

For the named parameter markers to be easily distinguished from normal
parameters, I think the keyword should be able to be a string or any
other scheme objects according to circumstances.

Examples:

(ranking 2 "Sting" 3 "mission impossible" 1 "Ben Hur")

(buy 'apple 'day 'low "price" 71.89 "qty" 1000)

(number->string 1234567 10 'pad-char #\0 'min-width 10)

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Joo ChurlSoo