Variables

= binds

The single equals sign is the match operator: it matches the value on the right against the pattern on the left. With a fresh name on the left, matching binds the value to that name.

name = "Ada" age = 36 IO.puts(name) # prints Ada IO.puts(age) # prints 36

Rebinding

You may bind a new value to the same name at any time, and the old value is simply gone. A match against a bound name can still fail: writing 1 = 2 raises a MatchError because 1 never matches 2.

x = 1 x = x + 1 IO.puts(x) # prints 2

Naming rules snake_case

Variable names start with a lowercase letter or an underscore, then use lowercase letters, digits, and underscores. Words join with underscores, a style called snake_case.

Names cannot start with a digit and cannot contain spaces or dashes. A leading capital letter would turn the name into an alias, which lesson 08 covers.

first_name = "Ada" score_2 = 10 IO.puts(first_name) # prints Ada

Pin with ^

The pin operator stops rebinding and turns the name into an assertion instead. The line below passes only because expected already holds 42.

expected = 42 ^expected = 42 # matches, nothing changes

A different number on the right would raise a MatchError rather than rebind. Reach for pin whenever an old value must stay exactly as it is.

Next: Numbers

Article author: Arthur Isaev