17.3. Pragma

Pragma is a modifier that enforces that its value must be evaluated at compile time. This is designed to be used as a guarantee that something is evaluated at compile time, such as calculating a complicated constant, reading a file or even testing.

17.3.1. Syntax

Pragma ::=  "pragma" ModifierValue

17.3.1.1. Examples

fibonacci_cache = [1, 1]

# Pre-fill fibonacci_cache with the first 200 values
pragma build_fibonacci_cache(200)

def build_fibonacci_cache(n:Int)
  i = 0
  while i < n
    # fibonacci auto-fills the cache
    fibonacci(i)
    i += 1
  end
end

# Naive cached fibonacci implementation
def fibonacci(n:Int)
  if n < fibonacci_cache.length
    return fibonacci_cache[n]
  else
    value = fibonacci(n - 1) + fibonacci(n - 2)
    fibonacci_cache[n] = value
    return value
  end
end

# Read a file at compile time
constants = pragma read("player_constants.txt").lines

const MAX_HEALTH = constants[0]
const MAX_ARMOUR = constants[1]
const MAX_SPEED  = constants[1]