Blocks and control flow

A block is a piece of code surrounded in braces ({...}). Blocks let you store code to run it later. To run the code in a block, use do:

greeting : {show "Hello, world!"}
do greeting

Hello, world!

Without do, the block will do nothing:

greeting : {show "Hello, world!"}
-- nothing happens

You can call do on a block multiple times:

greeting : {show "Hello, world!"}
do greeting
do greeting

Hello, world!
Hello, world!

You can write multiple lines of code in a block; the value of the block is the value of the last line:

sum : {
    show "calculating 1 + 2..."
    1 + 2
}

show (do sum)

calculating 1 + 2...
3

You don’t have to store a block in a variable before calling do:

sum : do {1 + 2} -- equivalent to `sum : 1 + 2`

Blocks are useful for logic and control flow. For example, if accepts a condition and two blocks. If the condition is True, the first block will be evaluated, and if it’s False, the second block will be evaluated.

secret : 5
guess : 3
if (guess = secret) {show "You win!"} {show "Try again"}

Try again

repeat accepts a number of times and runs the provided block that number of times:

repeat (3 times) {
    show "Hello, world!"
}

Hello, world!
Hello, world!
Hello, world!

It’s important to remember that blocks are values, just like text and numbers are — they can be stored in variables and passed to functions. repeat is just a function that accepts a block as input. You can build your types of control flow easily, and we’ll do just that in the next chapter!