On Sat, Feb 10, 2024 at 11:12:04AM +0000, siiky via wrote: > Hi Al, > > > On a practical level, I would be sad if vector-ref, for example, was > > "impure", and thus compiling a vector-ref invalidated all previously- > > checked globals for the current scope. Likewise, I would prefer to > > declare a procedure using vector-ref as pure, to let csc know that it > > does not modify globals (or the filesystem etc). > > The function vector-ref doesn't stop being pure (i.e. referentially > transparent) depending how you use it. The function is always referentially > transparent -- the expression (vector-ref some-global-vec) isn't. Quoting > from "Functional Programming in C++" by Ivan Čukić:
CHICKEN's type system differentiates between "pure" and "clean". A "pure" function has no side effects and will always return the same value given the same input (excluding the environment). A "clean" function does not modify any state, but may return different values at different times depending on the value. That's why vector-ref is marked as "clean" and not "pure" in types.db. A procedure like "not" and all type predicates are marked as "pure". Hope this clears things up a bit! Cheers, Peter
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