Eight instructions. No roadmap.
> < + - . , [ ]. That is the entire platform. There will be no ninth. We have been asked. We said no.
Features your organisation did not ask for
Full Gregorian compliance
Divisible by 4, except by 100, unless by 400. Implemented properly, not with the "every fourth year" shortcut that would have been right for 199 of the 200 years. We tested the shortcut. It got 307 dates wrong. All of them in 1900.
Judgemental validation
29 February 1900? INVALID. 31 April? INVALID. Hyphens? INVALID. FuckWhatDay never guesses, never normalises and never wraps your bad date into a good one. It just looks at you.
Clockless architecture
FuckWhatDay does not know what day it is today. This is not a limitation. It is a principled refusal to read your system clock, which you were using to know what day it was anyway.
Byte sized numerics
Every value fits in eight bits, because a year is stored as a century and a year in that century. 2026 is 20 and 26. This is how we cut costs.
Deterministic to a fault
The same input gives the same output, every time, on every interpreter we own (three, plus a compiler). No randomness, no environment, no state, no fun.
Seven enterprise output formats
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY and SUNDAY. Eight if you count INVALID, which we do, because it is our favourite.
Native Windows support
Each instruction is translated into the C statement that does the same thing, then compiled into a standalone exe. It is now Brainfuck at the speed of machine code, which is a sentence nobody needed.
Annotated source
The program ships with comments. The comments are not allowed to contain a full stop, a comma or a hyphen, because those are instructions. Writing documentation under these conditions builds character.
By the numbers
The first four are counted live, by this page, from the program it just downloaded. We could not make them up even if we wanted to. We wanted to.
...Brainfuck instructions
...loops, each one load bearing
...output instructions: exactly enough to spell seven weekdays, INVALID and one line feed
...input reads. Eight digits and a newline. Not one byte more
73,049dates tested. That is all of them
567,392instructions executed for the hardest date
0lines of Python involved in the calculation
0network requests. It cannot even spell network