Chapter 14 : Loops

General Iteration

ReasonLIGO is a functional language where user-defined values are constant, therefore it makes no sense in ReasonLIGO 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, ReasonLIGO loops are written by means of tail recursive functions

Here is how to compute the greatest common divisors of two natural numbers by means of Euclid’s algorithm:

let rec iter = ((x,y) : (nat, nat)) : nat =>
  if (y == 0n) { x; } else { iter ((y, x mod y)); };

let gcd = ((x,y) : (nat, nat)) : nat => {
  let (x,y) = if (x < y) { (y,x); } else { (x,y); };
  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).

1 type coordinates = (int, int, int) 2 type planet = { 3 name : string, 4 position : coordinates, 5 density : nat, 6 atmospheric_activity : bool 7 } 8 9 let star_map : list(planet) = [{ 10 name : “Earth”, 11 position : (0,0,0), 12 density : 20n, 13 atmospheric_activity : true 14 }, 15 { 16 name : “Jupiter”, 17 position : (2,7,1), 18 density : 340n, 19 atmospheric_activity :false 20 }, 21 { 22 name : “Methuselah”, 23 position : (2232,7423,12342), 24 density : 44n, 25 atmospheric_activity : false 26 }, 27 { 28 name : “Osiris”, 29 position : (134,454,1321), 30 density : 165n, 31 atmospheric_activity : true 32 }, 33 { 34 name : “Gliese”, 35 position : (234,8045,435), 36 density : 11n, 37 atmospheric_activity : true 38 }, 39 ] 40 // Type your solution below 41 let conditions = ((acc, p):(list(planet), planet)) : list(planet) => acc; 42 let scan = (l : list(planet)) : list(planet) => l; 43 44 let scan_results : list(planet) = scan (star_map);