Control Flow
Unlike many other scripting languages, Lamb doesn't have a concept of "truthy". As a consequence, values must be converted to booleans before being used in places where a boolean is expected, like if conditions.
If Expressions
In Lamb, the simplest control flow is an if expression. They look like this:
if <cond-1> {
<body-1>
} elif <cond-2> {
<body-2>
} else {
<body-3>
}
Unlike in many languages, there are no parenthesis requires around the conditions, so if true { } else { } is syntactically correct.
An if expression evaluates to the final value expression of the branch that is taken. If there is no else branch, and none of the branches are taken, the expression evaluates to nil.
Case Expressions
When looking to test if a variable is one of a series of values, one could write:
if val = 1 || val = 7 {
...
} elif val = 4 || value = 8 {
...
} else {
...
}
But if we want to extend this to arrays it gets messy:
-- Check if an array's first two elements are 1 and 2
if len(arr) > 2 && arr[0] = 1 && arr[1] = 2 {
...
} else {
...
}
Lamb offers a more concise way to do this through pattern matching with case:
case val {
1 | 7 -> {}
4 | 8 -> {}
_ -> {}
}
case arr {
[1, 2, ..] -> print("Has 1 then 2"),
_ -> print("Doesn't have 1 then 2"),
}
Patterns can be arbitrarily nested and you can even bind patterns to values. For example, to sum an array, one could write:
let sum := rec fn(xs) -> case xs {
[x, rest @ ..] -> x + sum(rest),
[] -> 0,
};
sum([1,2,3,4]);
This function looks at the structure of the array, and if the array contains at least one element, assigns the first to xand assigns the rest of the array the value rest.
The syntax for a case expression is roughly:
case <value> {
(<pattern> -> <body>)*
}
If <body> is a block expression, no , is necessary. Otherwise, it is required to put a ,.
Similarly to if, a case expression evaluates to the value of the branch that is taken, or nil if no arms are taken.
Loops
Ah loops... yeah... we don't do that here. Loops can be imitated through the use of recursion, so be prepared to have to rid your mind of loops ;)