Control Flow

If-Then-Else

if condition then true_branch else false_branch

if 5 > 3 then "yes" else "no"    # "yes"

Nested:

if x < 0 then "negative"
else if x = 0 then "zero"
else "positive"

As expression:

let abs = λ→ if ₀ < 0 then -₀ else ₀ in abs(-5)
# Result: 5

Match

See Pattern Matching for full coverage.

match ₀
  0 → 1
  n → n × factorial(n - 1)

Recursion

Direct recursion:

╭─ factorial : ℤ → ℤ
╰─ if ₀ ≤ 1 then 1 else ₀ × factorial (₀ - 1)

Tail recursion with accumulator:

╭─ factAcc : I64 → I64 → I64
╰─ if ₁ < 2 then ₀
   else factAcc (₁ - 1) (₁ × ₀)

╭─ main : I64 → I64
╰─ factAcc ₀ 1

Mutual recursion:

let rec even = λ→ match ₀
                0 → ⊤
                n → odd(n - 1) ;
        odd = λ→ match ₀
                0 → ⊥
                n → even(n - 1)
in even 10