Four

Four

Paradigm(s)	Functional
Designed by	vpzom
Appeared in	2018
Computational class	Unknown
Major implementations	https://git.vpzom.click/vpzom/four
File extension(s)	.4

Four is an esoteric, purely functional programming language.

• Only has three characters, all others are ignored: `4()`
• Operations are contained within parentheses, the first contained expression is the type. e.g. `(44(444))`
• `()` is Nil.

Examples

This is a simple program that outputs "Hello, world!" It's minimally optimized, and could almost certainly be made much smaller.

(4((4444444)(4(444)(((444)44)4(((444)44)44))))((4444444)(4(((444)44)(44444)(44((444)(444)4)))(44((444)44))))(((444)44)((4444444)(4(((444)44)(44444)(44((444)(444)4)))(4444)))((444)(444)4))((4444444)((((444)44)44)(((444)44)4(444444444))(4(44444)((444)44))))((4444444)(4(444444444)(4444)))((4444444)(444444444))((4444444)((((444)44)44)(((444)44)4(444444444))(4(444)((444)44))))((4444444)((((444)44)44)(((444)44)4(444444444))(4(44444)((444)44))))((4444444)((((444)44)44)(((444)44)4(444444444))(4(4444)((444)(444)4))))((4444444)(4(((444)44)(44444)(44((444)(444)4)))(4444)))((4444444)(((444)44)4(4(4444444)((444)44))))((4444444)(4((444)44)(444444444))))

Value Types

Four supports the following data types:

• Integer: Non-fractional numbers, created using the `4` literal or from various operations.
• Nil: A type representing nothing, created using the `()` literal.
• String: A string of 0 or more Unicode characters, created using "char code to string" and other operations.
• Function: A callable procedure, created using "function declaration". Usable as an operation.

Operations

ID	Operation	Description
0	function declaration	Takes one expression as a parameter, and returns a callable function form of it. Functions can be used as operations.
1	multiply	Takes any number of values and multiplies them, ignoring nils. If passed zero values, returns nil. Strings can be multiplied by integers for repetition.
4	add	Takes any number of values and adds or concatenates them, ignoring nils. If passed zero values, returns nil.
8	divide	Divides two numbers. If either value is nil, returns nil.
9	character from string	Takes a string and an integer, returns the character at the given index in the given string as a string.
12	conditional	Takes three values. If the first value is 4, the second is returned, otherwise the third is returned.
16	subtract	Subtracts two numbers. If either value is nil, returns nil.
24	char code to string	Interprets a number as a Unicode codepoint. Returns a string.
nil	get	Returns a function parameter by index.