A pure function is a function that, given the same input, will always return the same output and does not have any observable side effect.
splice. They are two functions that do the exact same thing - in a vastly different way, mind you, but the same thing nonetheless. We say
sliceis pure because it returns the same output per input every time, guaranteed.
splice, however, will chew up its array and spit it back out forever changed which is an observable effect.
splicethat mutate data. This will never do as we're striving for reliable functions that return the same result every time, not functions that leave a mess in their wake like
checkAgedepends on the mutable variable
minimumto determine the result. In other words, it depends on system state which is disappointing because it increases the cognitive load by introducing an external environment.
checkAgemay return different results depending on factors external to input, which not only disqualifies it from being pure, but also puts our minds through the wringer each time we're reasoning about the software.
minimumimmutable, which preserves the purity as the state will never change. To do this, we must create an object to freeze.
A side effect is a change of system state or observable interaction with the outside world that occurs during the calculation of a result.
A function is a special relationship between values: Each of its input values gives back exactly one output value.
5points to several outputs:
[(1,2), (3,6), (5,10)](It appears this function doubles its input).
xas the input and
yas the output:
argumentsobject as the input. When we learn about currying, we'll see how we can directly model the mathematical definition of a function.)
memoizefunction works just fine, though it doesn't cache the results of the http call, rather it caches the generated function.
attrswhich should be telling to say the least.
punchare all pure and therefore referentially transparent. We can use a technique called equational reasoning wherein one substitutes "equals for equals" to reason about code. It's a bit like manually evaluating the code without taking into account the quirks of programmatic evaluation. Using referential transparency, let's play with this code a bit.
decrementHP, we see that, in this case, punch becomes a call to decrement the