Backslash Calculus
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Backslash Calculus is a programming language invented by User:Tailcalled after reading this reddit comment.
Syntax
Backslash Calculus is based on lambda calculus, but it only uses two characters: backslash and space. This is the basic syntax:
E = \ \ E - abstraction
| \ \\ E E - application
| \\ - innermost variable
| \\\ - the variable one level more out
| ... - ...
Computational Class
Backslash Calculus is clearly Turing-complete, even if one ignores its simple translation to lambda calculus. Here are the SKI combinators:
S = \ \ \ \ \ \ \ \\ \ \\ \\\\ \\ \ \\ \\\ \\ K = \ \ \ \ \\\ I = \ \ \\
Alternative alphabets
Tailcalled imagined a few alternative alphabets for Backslash Calculus.
Unreadable
One can replace backslash with ' and space with ". The SKI combinators will look like this with that alphabet:
S = '"'"'"'"'"'"'"''"'"''"''''"''"'"''"'''"'' K = '"'"'"'"''' I = '"'"''
Brainfuck
One can change the syntax a bit to make Backslash Calculus look more like brainfuck:
E0 = + E1 -
| [ E0 E0 ]
| .
| ,.
| ,,. <- unary-ish
| ...
E1 = > E0 <
| [ E1 E1 ]
| .
| ,.
| ,,. <- unary-ish
| ...
The SKI combinators will look like this:
S = +>+[[,,..][,..]]-<- K = +>[,.]<- I = +.-