Chapter 14 : Loops

General iteration

CameLIGO is a functional language where user-defined values are constant, therefore it makes no sense in CameLIGO to feature loops, which we understand as syntactic constructs where the state of a stopping condition is mutated, as with “while” loops in PascaLIGO.

Instead, CameLIGO loops are written by means of a tail recursive function

Here is how to compute the greatest common divisors of two natural numbers by means of Euclid’s algorithm: While loops are defined as follows :

let rec iter (x,y : nat * nat) : nat =
  if y = 0n then x else iter (y, x mod y)

let gcd (x,y : nat * nat) : nat =
  let x,y = if x < y then y,x else x,y in
  iter (x,y)

Your mission

1- Check the proposed code in the editor. Notice that we created a star map as a list of planet records.

2- Notice the unimplemented scan function. Suppose this function is called from the main function with the star_map variable as its input l. Iterates through each record of the list (seen in Chapter Lists) in order to find a planet that respects specified conditions (see step 3).

3- Define a function conditions which computes in an accumulator the list of planet verifying some conditions: density superior to 100 and atmospheric_activity true. If conditions are met, the function conditions adds this planet to the accumulator. Don’t forget to cast the initial value of the accumulator (as a list of planet).

type coordinates = (int * int * int) type planet = { name : string; position : coordinates; density : nat; atmospheric_activity : bool } let star_map : planet list = [{ name = “Earth”; position = (0,0,0); density = 20n; atmospheric_activity = true }; { name = “Jupiter”; position = (2,7,1); density = 340n; atmospheric_activity = false }; { name = “Methuselah”; position = (2232,7423,12342); density = 44n; atmospheric_activity = false }; { name = “Osiris”; position = (134,454,1321); density = 165n; atmospheric_activity = true }; { name = “Gliese”; position = (234,8045,435); density = 11n; atmospheric_activity = true }; ] // Modify the code below let conditions (acc, p: planet list * planet) : planet list = acc let scan (l : planet list) : planet list = l let scan_results : planet list = scan star_map