Control Flow

if Expressions

Example:

int foo = 23

if foo > 100 {
    print('foo > 100')
    
} else if foo > 20 {
    print('foo > 20')
    
} else {
    print('else handle')
}

A space is required between else and if. The expression part expr following if must be of boolean type; implicit type conversion is not supported. Parentheses are not needed after the if.

To explicitly type-cast the value to a boolean, you can use as, like so: if foo as bool {}. Here, false/0/null will be converted to false, and all other expressions will be converted to true.

print/println are built-in functions designed mainly for debugging. They only support string/bool/number types and separate multiple arguments by commas. No formatting functionality is included.

for Expressions

Classic Loop

var sum = 0
for int i = 1; i <= 100; i += 1 {
    sum += i
}
println('1 +..+100 = ', sum)

After compilation and running, the output should be:

> nature build main.n && ./main
1 +..+100 = 5050

❗️ In Nature, there's no ++ syntax; use i += 1 instead of i++. Parentheses are also not required after the for.

Conditional Loop

Here's another example using the sum 1+..+100:

var sum = 0
var i = 0
for i <= 100 {
    sum += i
    i += 1
}

println('1 +..+100 = ', sum)

If compiled correctly, the output should be the same as that of the classic loop. The expression following for needs to be of boolean type for the loop to work.

💡 This is similar to the while loop in C language, but Nature integrates it under the for keyword.

Iteration Loop

Let's take a look at the syntax:

var list = [1, 1, 2, 3, 5, 8, 13, 21]

// When iterating over a vec structure, it generates v
for v in list {
    println(v)
}

var map = {1:10, 2:20, 3:30, 4:40}

// When iterating over a map structure, it generates k
for k in map {
    println(k)
}

// If you need both k and v, simply generate two variables
for k,v in list {
    println(k, v)
}

Iteration is for traversing vec/map/string types and currently only supports these three types. Note that k, v here is syntactic sugar for variable declaration. The complete, conceptual syntax should be for var (k,v) in list, which is omitted for simplicity.

Also, the scope of k and v is limited to the loop body. So, code like this will not cause conflicts:

var k = 1 
for k,v in list { 
    // ...
} 

Loop Interruption and Skip

The break keyword is used to exit the current loop, and continue skips the current iteration and moves directly to the next loop evaluation. Here's how you use them:

var list = [1, 1, 2, 3, 5, 8, 13, 21]
var sum = 0
for k, v in list {
    if sum > 20 {
        break
    }
    sum += v
}
println(sum)


var sum2 = 0
for int i = 0; i < 100; i += 1 {
    if i % 2 == 0 {
        continue
    }

    sum2 += i
}
println(sum2)

The compiled output would be:

> nature build main.n && ./main
33
2500