Learning Perl 6

Chapter 5. Building Blocks

Blocks are the thingys that group multiple statements into a single thingy. You’ve already used some of them, based on the faith I asked you to have in the introduction. Now it’s time to look at those more closely. This chapter covers the basics and works up to simple subroutines. You’ll see just enough here to get you through the next couple of chapters, then quite a bit more in Chapter 11.

Blocks

A Block is a group of statements surrounded by braces. You’ve already used loop to repeat a group of statements. You also used the if-else structure, which used a Block in each branch and executed only one of them:

loop { ... }

if $n %% 2 { put "Even!" }
else       { put "Odd!"  }

A bare block is one that has nothing around it. It is in sink context because you do nothing with its result. It provides a scope and runs once immediately. The result is the last evaluated expression (not necessarily the last lexical expression) in the Block. Here’s a simple one that does nothing:

{ ; }

Note

There’s a bit of discouraged syntax that’s just {}. It constructs an empty hash (Chapter 9). With a statement separator inside the braces the compiler recognizes it as a Block.

Here, you can’t tell which expression your program will evaluate last until the Block knows what time it is. now is a term that gives the current time, which you can coerce to an Int:

{ now.Int %% 2 ?? 'Even' !! 'Odd' }

Sometimes you’ll get Even and sometimes you’ll get Odd. However, since you do nothing with the result, ...