882 Replace fn:chain by fn:compose #1883
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michaelhkay
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ChristianGruen
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Discussed on 2025-03-18, discussion timed out. Generally the fn:compose spec is regarded favourably but there was pushback against dropping fn:chain. |
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Drops the existing fn:chain function and replaces it with a new fn:compose function.
This combines two separate changes:
(a) whereas fn:chain applies a sequence of functions to an input, fn:compose returns a composite function that can be used repeatedly with different inputs.
(b) the fn:compose function is restricted to arity-1 functions, which leads to a much simpler specification that still handles the vast majority of practical use cases.
In particular, note that if the sequence of functions to be applied is statically known, then it can always be written out explicitly; the real use case for this function is when the sequence of functions is constructed dynamically. And in this situation, fn:chain in its current form can easily fail because of problems with the arity of the functions included in the chain.