Is generic dispatch okay even though it mutates a datastructure, because it's just mutating the toplevel in a mutating-during-hacking kind of way?
The talk I linked earlier today was largely (but not entirely) an advocacy for generic dispatch.
Yes. This is one of those implementation vs. semantics things. You could say that a procedure definition also mutates a data structure (the current module, in Guile), but we wouldn't consider this a side-effect or otherwise "impure".
David Thompson at 2016-01-15T00:19:15Z
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