```catala
declaration scope S:
  output x content integer

scope S:
    definition x equals 0

# Map
    assertion (i + 2) for i among [1; 2; 3] = [3; 4; 5]

# Filter
    assertion (list of i among [1; 2; 3] such that i >= 2) = [2; 3]
    assertion ((i + 2) for i among [1; 2; 3] such that i > 2) = [5]

# Sum
    assertion sum integer of [1; 2; 3] = 6
    assertion sum integer of (i + 2) for i among [1; 2; 3] = 12

# Count
    assertion number of [1; 2; 3] = 3
    assertion (number of list of i among [1; 2; 3] such that i >= 2) = 2

# Extremum
    assertion maximum of [1; 2; 3] or if list empty then 10 = 3
    assertion maximum of (decimal of i) for i among [1; 2; 3] or if list empty then 10. = 3.

# Arg extremum
    assertion (content of i among [1; 2; 3]
                 such that decimal of ((2 - i) * (2 - i)) is minimum
                 or if list empty then 42)
              = 2
```



```catala-test-inline
$ catala Typecheck --check-invariants
┌─[RESULT]─
│ All invariant checks passed
└─
┌─[RESULT]─
│ Typechecking successful!
└─
```

```catala-test-inline
$ catala scopelang -s S
let scope S (x: integer|internal|output) =
  let x : integer = error_empty ⟨ ⟨true ⊢ ⟨0⟩⟩ | false ⊢ ∅ ⟩;
  assert (map (λ (i: integer) → i + 2) [1; 2; 3]) = [3; 4; 5];
  assert (filter (λ (i: integer) → i >= 2) [1; 2; 3]) = [2; 3];
  assert (map (λ (i: integer) → i + 2)
            filter (λ (i: integer) → i > 2) [1; 2; 3])
         = [5];
  assert (reduce
            (λ (sum1: integer) (sum2: integer) → sum1 + sum2)
            0
            [1; 2; 3])
         = 6;
  assert (reduce
            (λ (sum1: integer) (sum2: integer) → sum1 + sum2)
            0
            map (λ (i: integer) → i + 2) [1; 2; 3])
         = 12;
  assert (length [1; 2; 3]) = 3;
  assert (length filter (λ (i: integer) → i >= 2) [1; 2; 3]) = 2;
  assert (reduce
            (λ (max1: integer) (max2: integer) →
             if max1 > max2 then max1 else max2)
            10
            [1; 2; 3])
         = 3;
  assert (reduce
            (λ (max1: decimal) (max2: decimal) →
             if max1 > max2 then max1 else max2)
            10.
            map (λ (i: integer) → to_rat i) [1; 2; 3])
         = 3.;
  assert (let weights : list of (integer, decimal) =
            map (λ (i: integer) →
                 (i, let i1 : integer = i in
                     to_rat ((2 - i1) * (2 - i1))))
              [1; 2; 3]
          in
          reduce
            (λ (x1: (integer, decimal)) (x2: (integer, decimal)) →
             if x1.1 < x2.1 then x1 else x2)
            let i : integer = 42 in
            (i, let i1 : integer = i in
                to_rat ((2 - i1) * (2 - i1)))
            weights).0
         = 2
```

```catala-test-inline
$ catala test-scope S
┌─[RESULT]─
│ x = 0
└─
```