li1I

why

— everyone whom I have shown this to

li1I is a domain-specific programming language for integer calculations. It supports recursive functions, conditional execution, and expresses arithmetic in Reverse Polish notation.

The only valid characters in an li1I program are l, i, 1, I and whitespace. There is no syntax for comments. Comments are not necessary in a language of such clarity.

This repository contains both a definition of the li1I language and an implementation based on LLVM 10 which supports interpretation through a JIT compiler and AOT compilation for linking with other programs.

Language

Program

An li1I program consists of the token li1I followed by any number of functions enclosed in braces. Left brace is spelled l1iI and right brace is spelled l1Ii. Here is an empty program:

li1I
l1iI

l1Ii

Beautiful.

Literals and Identifiers

Function identifiers are of the form I[iI1l]*.

Variable identifiers are of the form i[iI1l]*.

The only type supported in li1I is an integer. I don't know how big the integral type is and I can't be bothered checking. The value of an integer is given by the length of a string of 1s. E.g. 1 has the value 0, 11 has the value 2, 1111111111 has the value 10 and so on.

Functions

A function is indicated with the token lI1i, which is followed by a function identifier, any number of variable identifiers (parameters), then a brace-enclosed block.

In that brace enclosed block, any number of statements are allowed.

Statements

A statement is an expression followed by the token l1ii.

Expression

An expression can be:

• The name of a variable, which evaluates to its value.
• A variable declaration, spelled liI1 <variable identifier> lIi1 <expression>, which evaluates to the value of the initialiser.
• A function call, spelled <function identifier> li1l <expression>* lil1, which evaluates to the result of the function call.
• An arithmetic or logical expression (see below).
• A conditional expression (see below).

Arithmetic and Logical Expressions

Arithmetic and logical expressions in li1I are written in Reverse Polish notation.

The following arithmetic operations and their spelling in li1I are:

• Addition: llli
• Subtraction: llii
• Multiplication: liil
• Integer division: llil
• Exponentiation: liii

The following logical operations and their spelling in li1I are:

• Greater than: ll1i
• Less than: ll1I
• Equality: ll11
• Inequality: l111

Conditional Expressions

A conditional expression is of the form:

l1i1 li1l <arithmetic or logical expression> lil1
l1iI
        <then statements>*
l1Ii 
l1il l1iI
        <else statements>*
l1Ii

Is a then with no else supported? Who knows.

Examples

Here's what a factorial function looks like:

li1I
l1iI
        lI1i I li1l i lil1
                l1i1 li1l i 11 ll11 l1ii lil1
                        11 l1ii
                l1il
                        i 11 llii I i liil l1ii
                l1ii

        lI1i IIII
                liI1 i lIi1 11111111111 l1ii
                I l1ii
l1Ii

Compiler

The compiler supplied in this repository is also called li1I and is based on LLVM 10. It supports interpretation through JIT compilation and also AOT compilation to an object file (which you'll need to link using your system linker).

Usage

l1iI <input file> [<flags>]

Flags:

• -o <file>: Write output to file
• -e: Execute the program immediately
• -c: Compile to an object file
• --emit-ast: Emit l1iI AST files for source inputs
• --emit-llvm: Emit the LLVM representation for assembler and object files
• --emit-tokens: Emit lexer tokens

Object files output by l1iI depend on libc, so you'll want to link them like so:

l1iI factorial.li #outputs factorial.o
gcc factorial.o -o factorial

Building

The build system is written in CMake. If you have the development libraries for LLVM 10 available you should be able to mkdir build && cd build && cmake .. && make -j or whatever. I tested it on Ubuntu version somethingorother, it might work on Windows, idk.