ghūl programming language

ghūl (pronounced 'ghoul') is a statically typed programming language for .NET 10. The compiler is about 120,000 lines of ghūl, and compiles itself.

Every example on this site is a whole program. Press edit & run, change it, and run it in your browser.

drawing: a fractal tree

ghul

use System.Math

use Raster.IMAGE

let spread = 0.4D

let shrink = 0.76D

let image = IMAGE(500, 500)

branch(

x: double, y: double,

angle: double, length: double,

depth: int

) is

if depth == 0 then

return

fi

let tip_x = x + length * Math.cos(angle)

let tip_y = y + length * Math.sin(angle)

image.stroke(0.6D * cast double(depth))

image.line(x, y, tip_x, tip_y)

branch(tip_x, tip_y, angle - spread, length * shrink, depth - 1)

branch(tip_x, tip_y, angle + spread, length * shrink, depth - 1)

si

image.view(0.0D, 0.0D, 500.0D, 500.0D)

image.colour(60ub, 40ub, 20ub)

branch(250.0D, 10.0D, Math.pi / 2.0D, 110.0D, 10)

image.write("tree.png")

image.show("tree.png")

<<image tree.png>>

tree.png

where to go next

• Rosetta Code - 703 tasks solved in ghūl, searchable, and nearly all runnable here. The page opens on one picked at random.
• the tour - the language a topic at a time, every example editable.
• getting started - ghūl on your own machine. A ghūl repository pins the compiler as a local .NET tool, so the compiler arrives with the code.

what is distinctive

• type narrowing - a value's type follows control flow. A null test, an isa, a union variant test or an if let narrows whatever was tested - a local, a field, or a whole member-access path - and the narrowing survives the calls the compiler can show leave it alone.

• everything is an expression - if, case, loops and blocks all yield values. A for loop that finds something evaluates to what it found.

• unions and pattern matching - refutable patterns match by type and by value, and a case over a closed domain - a union, an enum, bool, a closed class hierarchy, a tuple of those - is checked for coverage.

• keywords, not braces - blocks open with a keyword and close with its mirror: is ... si, if ... fi, do ... od. No semicolons at the end of a line.

The rest is what you would expect of a .NET language: classes, structs, traits and generics, first-class functions and closures, generators, async/await, and every NuGet package. ghūl produces ordinary assemblies and packages, and other .NET languages can call them.

The language is under active development: whatever the compiler accepts is the definitive reference.