Logos Programming Language (WIP)

Build

Requirements

• C++ compiler
• LLVM 19
• cmake

Linux

Mac

Windows

Not working yet.

Overview

Hello world

main() {
    print("Hello world")
}

Variable Declaration

main() {
    // Implicit typing
    x = 3
    y = 4
    z = x + y
    print(z)
    
    // Explicit typing
    x: Int = 3
    y: Long = 4
    z: Float = y / 3
    print(z)
}

Unary and Binary Operations

main() {
    a = (1 + 4) - (6 * 5) / 2
    b = a % 5
    d = 0
    d++
    d--
}

Statements Block

Statements Block is a collection of statements wrapped in curly braces and can be part of a function, for loop, if statement, etc. If only one statement exists in the block, you can omit the braces altogether (similar to C/C++).

// Block with multiple statements and braces - valid
main() {
    x = 3
    y = 4
}

// Block with one statement without braces - valid
main() print("Hello world")

// Block with multiple statements without braces - invalid!
main() 
    x = 3
    y = 4

If Statement

main() {
    x = 3
    y = 4
    if x > y {
        print("x is greater than y")
    } else if x < y {
        print("x is less than y")
    } else {
        print("x is equal to y")
    }
}

Pattern Matching

enum Enum {
    ENUM1
    ENUM2
    ENUM3
}

main() {
    e = Enum.ENUM1
    switch e {
        ENUM1: { print(ENUM1) }
        ENUM2: { print(ENUM2) }
        ENUM3: { print(ENUM3) }
    }
    
    str = "some string"
    switch str {
        "some string": print("some string")
        "other string": { print("other string") }
        else: { 
            print("default string") 
        }
    }
}

Range Loop

To iterate over an index, use the range loop. The range loop has one variable loop, usually named 'i'.

main() {
    x = 10
    for i in 5..x {
        print(i)
    }
}

Or

main() {
    x = 10
    for i in ..x {
        print(i)
    }
}

Or even (more on for.i below).

main() {
    for 10 {
        print(for.i)
    }
}

Foreach Loop

main() {
    arr = [1, 2, 3]
    for element in arr {
        print(element)
    }
}

Infinite Loop

main() {
    for.ever {
        print("In infitine loop")
        if true break
    }
}

Meta Variables

In Logos, there are special variables called Meta Variables that are namespaced with a keyword, for example, 'for.i'. These variables will be automatically created and assigned a value once you will declare them.

for.i

In for loops, you don't have to necessarily define an i variable for iteration. Logos will generate it for you using the meta variable 'for.i'. For example

main() {
    for 10 {
        print(for.i)
    }
}

Prints:

0
1
...
8
9

for.isFirst and for.isLast

Likewise, you can hook into the first and last iteration of a loop using the for.isFirst and for.isLast variable instead of calculating the index yourself.

main() {
    for i in 5..x {
        if for.isFirst {
            print(i)
        }
        if for.isLast {
            print(i)
        }
    }
}

Prints:

5
9

Control Flow

If Statement

If statements are done using the 'if', 'if else' and 'else' keyword, similar to other languages like Java, Go or C/C++. In Logos you don't have to wrap the condition in parenthesis.

func() {
    a = 3
    if a > 2 {
        return
    }
    if a == 5 {
        return
    }
    if a <= 9 {
        return
    }
}

main() {
    func()
}

Sometimes you want to break from nested if statements. In Logos you can do this using 'break if' which will break from the outermost if. For example:

main() {
    if true {
        if true {
            print("inside nested if")
            break if
        }
        print("inside if")
    }
}

Prints:

inside nested if

If Macro

tbd

The defer keyword

Similar to other languages, you can delay the execution of a function using the 'defer' keyword. For example

func(str: Str) {
    print(str)
}

main() {
    defer func("After")
    func("Before")
}

Prints:

Before
After

The io keyword

The second mechanism to handle IO connections is with the io keyword. With this mechanism you pass a pair of function names, like so:

io(openFile, closeFile)

where the left function will be the opening function and the right function will be the closing function. Now, once the io is declared, you can call the opening function (left-hand) with the io keyword, for example

io f = openFile() {
    // Do something
    // text = f.read()
} 

And you are done. You don't need to call closeFile. Logos will do it for you. Everytime you call the opening function with the io keyword, the closing function will be called at the end of the scope, making sure your resources are being freed correctly.