functions

# Functions: `def`, typed parameters, a typed result.

def add(a : Int32, b : Int32) : Int32
  a + b
end

# The last expression is the result. There is no `return` needed.
def describe(n : Int32) : String
  if n < 0
    "negative"
  elsif n == 0
    "zero"
  else
    "positive"
  end
end

# Parameters can have defaults, and callers can name them.
def greet(name : String, greeting = "Hello") : String
  "#{greeting}, #{name}!"
end

puts add(2, 3)
puts describe(-5)
puts greet("Ayşe")
puts greet("Ayşe", greeting: "Selam")

Press Run.

recorded with iyi 0.18.0 (built on Crystal 1.22.0-dev [2a9653052] (2026-10-18)) · Linux 7.0.0-38-generic x86_64, QEMU Virtual CPU version 2.5+ · 2026-10-19

You can type in the pane: nothing here compiles, so what you type cannot run, and the page says which bytes it is running the moment the text stops being the recorded file. There is no standard input, no filesystem and no threads on this target, and one sample fails on purpose for exactly that reason.

Run executes functions.wasm, the module the compiler built from this file, in your browser. How this works

$ iyi run functions.iyi