Control Flow

In Seal, control flow is straightforward. It has off-side rule aka indentation rule for defining where blocks start and end like Python, CoffeeScript, ABC.

If-Else

if a > 0
    print("a is positive")
else if a < 0
    print("a is negative")
else
    print("a is zero")

You just use indentation to define blocks. No : unlike Python.

a = integer(read())

if a == 0 then print("zero")
else if a == 1
    print("it is one")
else if a == 2 then print("two")
else print("unknown")

You can mix inline if-else statements with block ones.

While

while true
    print("this will print forever")

While loop is straightforward as well.

while true do print("hello")

You can write inline while loop with do keyword.

Seal-style loop

i = -1
max = 10
while ++i < max
    print(i) 

Instead of putting ++i at the end of the loop body, you can put the increment into the condition check itself, and compensate by assigning -1 to i before the loop begins. So it becomes kind of a "C-style for loop". If you'll let me, I want to call this "Seal-style loop".

For

for i in 10
    print(i) // from 0 to 10 (10 is excluded)

for c in "my string"
    print(c)

for x in [1, 2, 3, 4, 5]
    print(x)

Currently, for loop supports 3 types of iterables: integer, string and list.

sum = 0
for i in 10 do sum += i
print(sum)

Here is inline for loop as well.

Skip and Stop

for c in "Hello, World!"
    if c == "l" then skip
    if c == "r"
        stop

    print(c)

Output:

H
e
o
,

W
o

As you can tell, skip is for the traditional continue keyword, and stop is for break. I have used these keywords since the first version of Seal, and decided to keep them. Because why not?

Function

define is_odd(n)
    return n % 2 == 1

This code defines a local function called "is_odd" in current scope.

is_odd = define(n)
    return n % 2 == 1

Since functions are first-class citizens in Seal, you can create an anonymous function and assign that directly to a variable. For convention, first option is more recommended.

define optimized_is_odd(n) (n & 1) == 1

If closing parenthesis is followed by a single expression right away, it is called "lambda".

add = define(a, b) a + b

Again, first-class.

define $add(a, b) a + b
$add = define(a, b) a + b

define $add(a, b)
    return a + b

$add = define(a, b)
    return a + b

By putting $, you define that function as global.

Include

include "io"

Include statement requires string after it. Here are standard library names:

• "math"

• "io"

• "system"

When you include a file, you get capital case named global variable as a convention.

include "math"
Math // global hashmap holding mathematical functions
include "io"
IO  // again, global hashmap holding IO-related functions
include "io"  //  does not load again

When include statement is executed, first, it looks for standard libraries. Then, local files. It can include both so, dll files or Seal scripts. It starts with shared object files, and then Seal files. It loads the file only once.