Here's a macro that generalizes the two 'threading' macros -> and ->>.
It works by using the idea of 'nesting marker' (from Oz) to specify
where the result of the previous form should be nested in the
subsequent form.
(defmacro -$>
"Threads the expr through the forms. Inserts x into
the first form at the position marked by the $ symbol.
If the second form is not a list then it behaves as ->.
If there are more forms, inserts the first form into the second
form at the position marked by the $ symbol, etc."
([x form] (if (seq? form)
(let [split (split-with (partial (complement =) '$)
form)]
`(~@(first split) ~x ~@(rest (second split))))
(list form x)))
([x form & more] `(-$> (-$> ~x ~form) ~...@more)))
If this is any use to anyone (esp. anyone who has a CA) then consider
it public domain.
Any improvements appreciated!
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