Basic Example

This is a very basic example of using Vapour in the hope it helps you get started, We'll create a function to create the Fibonacci sequence.

Create a directory and place a script.vp file in it.

func fibonacci(n: int): int {
  let a: int = 0
  let b: int = 1
  let sequence: int = ()
  
  for(let i:int in 1..n) {
    sequence <- c(sequence, a)
    let next_num: int = a + b 
    a = b
    b = next_num
  }

  return sequence
}

• We declare the function with the func keyword.
• We give parameter n the int type (integer)
• We indicate that the function returns a vector of integers.
• We indicate that the function returns a vector of integers.
• We declare sequence as an empty vector with ()
• We range over with .. where in R we do it with :

info

If you typed the above in your editor you will have noticed a warning already.

You can then call the function once it's declared.

# ... function declaration
fibonacci(10)

Once that done we are ready to run the script! Run the command below from the terminal, the -run-only flag has Vapour run the script and not generate the corresponding R file (we'll do that later).

vapour -infile=script.vp -run-only

[HINT]	file vapour.vp, line 6, character 24: `n` might be missing
[INFO]	file vapour.vp, line 6, character 10: `i` is never used

Running the command display an INFO and a HINT, indeed the i variable declared in the for loop is never used but importantly the n variable (the function variable) might be missing since it has no default value.

Running the code below will fail because n is missing.

fibonacci()

We can easily fix that issue, either add a check for missing or give the function a default value.

Default value

func fibonacci(n: int = 5): int {
  let a: int = 0
  let b: int = 1
  let sequence: int = ()
  
  for(let i:int in 1..n) {
    sequence <- c(sequence, a)
    let next_num: int = a + b 
    a = b
    b = next_num
  }

  return sequence
}

Missing check

func fibonacci(n: int): int {
  stopifnot(!missing(n))

  let a: int = 0
  let b: int = 1
  let sequence: int = ()
  
  for(let i:int in 1..n) {
    sequence <- c(sequence, a)
    let next_num: int = a + b 
    a = b
    b = next_num
  }

  return sequence
}