Conditionals

In Grain, there are two main types of conditional statements: if and match. These allow you to make decisions based on values or the structure of your data.

If

The if statement works like in most languages, and else is optional:

let condition = true
 
if (condition) print("Condition is true")

You can also chain else if clauses:

let a = 5
if (a > 10) print("Greater than 10")
else if (a > 3) print("Greater than 3")
else print("3 or less")`

When using if as an expression that returns a value, every branch must return a value of the same type:

let value = if (true) 1 else 2
print(value) // 1

Failing to provide an else in this context would result in a type error, because the if expression wouldn’t be guaranteed to produce a value.

NOTE: This also allows if to fill the role of ternaries in other languages.

Match

Pattern matching lets you branch on both values and data structures.

Simple Value Matching

A simple match statement is extremely similar to a switch in other languages:

let x = 2
 
match (x) {
  1 => print("One"),
  2 => print("Two"),
  _ => print("Other")
}

Matching Patterns

Even with simple values and lists, match can handle complex branching logic cleanly. Unlike if statements, which require multiple nested conditions, match lets you clearly separate each case.

For example, you can mix different conditions on lists in one statement:

let input = [1, 2, 3]
 
match (input) {
  [1, _, _] => print("Starts with 1"), // Matchs the first valid branch.
  [_, 2, _] => print("Second element is 2"),
  [_, _, 3] => print("Ends with 3"),
  _ => print("Other pattern")
}

Here, a single match expression checks multiple aspects of a concrete array without nested if statements. This makes your code easier to read, maintain, and reason about as your program grows.

Tip: Later, with Patterns, you’ll be able to destructure more complex data structures concisely—turning match into one of the most expressive tools in Grain.