All junior devs should read OCs comment and really think about this.
The issue is whether is_number() is performing a semantic language matter or checking whether the text input can be converted by the program to a number type.
The former case - the semantic language test - is useful for chat based interactions, analysis of text (and ancient text - I love the cuneiform btw) and similar. In this mode, some applications don’t even have to be able to convert the text into eg binary (a ‘gazillion’ of something is quantifying it, but vaguely)
The latter case (validating input) is useful where the input is controlled and users are supposed to enter numbers using a limited part of a standard keyboard. Clay tablets and triangular sticks are strictly excluded from this interface.
Another example might be is_address(). Which of these are addresses? ‘10 Downing Street, London’, ‘193.168.1.1’, ‘Gettysberg’, ‘Sir/Madam’.
To me this highlights that code is a lot less reusable between different projects/apps than it at first appears.
This is true for only red and green loght detecting proteins (opsins) - the blue opsin gene is on chromosome 7.
The red and green detecting proteins have an interesting history in humans.
Fish, amphibians, lizards and birds have 4 different opsins: for red, green, yellow and blue colours. And the blue opsin sees up into the ultra-violet. Most animals can see waaaay more colours in the world than we (or any mammal) can. So what happened that makes mammal vision so poor?
It’s thought that all mammals descend from one or a few species of nocturnal mammal that survived the catastrophe that wiped out the dinosaurs at the end of the Cretaceous. The colour detecting cells (the cones) need a lot of light compared to ones that see in black-and-white (the rods) and therefore nocturnal animals frequently lose cones in favour of the more sensitive rods for better night vision. The mammals that survived the Cretaceous extinction had also lost the green and yellow opsins while keeping red and blue - basically the two different ends of the light spectrum.
Consequently today most mammals still have only 2 opsins so your cat or dog is red-green colourblind.
Why do humans see green? Probably because our monkey forebears, who lived in trees and ate leaves, needed to distinguish red leaves and red fruit (visible to birds) from the green background.
But how did we bring back the green opsin? A whole section of the X chromosome (where the red opsin is coded) got duplicated in a dna copying mistake and then there were two genes for red opsins. As there are different alleles (versions), they could be selected for independently and so one red opsin drifted up the spectrum to be specific for green. So our green opsin is a completely different gene to the green opsin in fish, birds, etc. This kind of evolution happens a lot which is why, for example, there are many families of similar hormones like testosterone and estrogen. And steroids too.