Pure functions? What the heck are those ?!?!

What is the basis for reason? And mathematics?

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Skepdick
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Joined: Fri Jun 14, 2019 11:16 am

Pure functions? What the heck are those ?!?!

Post by Skepdick »

Mathematicians keep talking about "pure" functions. A pure function is a function that has no external input and no external output (no side-effects). What incoherent nonsense is this?

An Input is the universe affecting the function.
An output is the function affecting the universe.

Inputs/Outputs ARE side-effects!

If we use Python as a model of computation this is a pure function, but it does nothing:

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   def f(): pass # Mathematical equivalent unknown 
This is NOT a pure function. It has outputs.

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   def g(): return 1 #Mathematical equivalent f() = 1 
This is NOT a pure function. It mandates input.

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   def h(x): pass # Mathematical equivalent unknown 
This is NOT a pure function - it mandates input and produces output:

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   def j(x): return x. # Mathematical equivalent f(x) = x 
This is a pure function. It calculates the answer to 2+2, but doesn't give you the answer.

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   def k(): 2+2 # Mathematical equivalent unknown 
If one takes an extensional view of functions, thereare no such things as pure functions!

Mathematicians, do you even know what you are talking about when you talk about "pure functions"?
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