Conditional (if then else)

A conditional expression is of the form

if expression then
    expression
else if expression then
    expression
...
else
    expression
end

An if then else expression returns the value from one of its branches depending on the test expression. For example

define max(a, b) =
    if a > b then a else b end;

An if can be written everywhere an expression is expected. For example

let
    multiplier = if turbo = "yes" then 1.5 else 1 end
in
    multiplier * base_velocity
end