Your first program

Put this in hello.sysl, anywhere you like:

print("Hello, sysl!")

var width = 6
var height = 7
print("area =", width * height)

Run it:

sysl run hello.sysl

(From a source checkout instead of an installed binary, that is sbt "syslJVM/run run hello.sysl".)

Hello, sysl!
area = 42

What is not there

No main. No imports. No class wrapped around the statements to give them somewhere to live. A sysl file is a module, and statements written at its top level run in order — so the smallest program is the code you actually meant to write.

A main is available when you want one, and you want one as soon as you care about the program’s arguments:

main(args: []string)
    print("started as:", args[0])
    print(args.len - 1, "argument(s) given")

print came from sysl, the standard module — the one module a file may write the names of without importing it, because it holds what the language desugars onto. It takes any number of arguments, converts each one to text, and separates them with spaces.

What the compiler did

run is one command of several, and it did four things in a row: parsed and checked the source, emitted textual LLVM IR, handed that to clang to assemble and link against the standard library archive, and ran the binary that came out. The binary is real — there is no interpreter and no VM underneath it.

build stops after producing that binary instead of running it, and test runs the @test functions in a directory. The tour uses run throughout.

Where to go next

The tour starts here and builds up. It is meant to be read in order, and every program in it is one you can paste into a file and run.

The command line is the other direction: the rest of the subcommands, the flags they share, and what each one leaves as an exit status. Nothing in the tour needs it.