KittenScript

KittenScript is a high-level explanatory programming language written in python3.7.

Block in KittenScript like lua.

Install

First, you need python>=3.6 and pip or git.
Then, use pip or git install it:

Use pip:

pip install -U KittenScript

Use git:

git clone https://github.com/stripepython/KittenScript/
cd KittenScript
pip install -r requirements.txt
python setup.py install

Test if installed well:

python -m KittenScript -v

Run

Use KittenScript/__main__.py.

Usage: python -m KittenScript [OPTIONS] FILE

Options:

-v, --version  Show the version and exit.    
-i, --ide      Show the IDE in English and exit.    
-ic, --ide-cn  Show the IDE in Chinese and exit.   
-s, --stdio    Enter interactive programming.    
--help         Show this message and exit.    

And use python -m KittenScript FILE to run file.
Like this:

python -m KittenScript test.kst

Basic grammar

Arithmeter

Same as all mainstream programming languages:

For example:

1 + 1
(2 + 3) * 4
7 + 6 * 5 > 2 == true

Booleans

Two keywords: true and false.

Lists

For lists, KittenScript is the same as Python:

[]
[1, 2, 3]
[1, "2", true]  # Support different types
[[1, 2, 3], [4, 5, 6]]   # 2D List
[[[1, 2], [3, 4]], [[5, 6], [7, 8]]]  # 3D List
# Can wrap
[
    "apple",
    "banana",
    "strawberry",
    "watermelon"
]

Dictionaries(Dict)

For dictionaries, KittenScript is the same as Python too:

{}
{'first': 1, 'second': 2}
# Can wrap
{
    'perfect': 2,
    'good': 1,
    'bad': 0
} 

Strings

For strings, KittenScript is similar to python2. You can use ", ' or "`".

''
"12345"
'Hello, World!'
`\n`  # Likes "\\n"

"Test\nTest\t"
'\''

Variables

Use var keyword to define a variable:

var a = 1
var b = 0.3 + 9.0
var c = var d = [1, 2]

If you use CONST_ prefix, it will be a const variable.
When the const variable is defined in this namespace, you can't redefine it.

var CONST_PI = 3.14

var CONST_PI = 3.1415926  # Error!

You can use +=, -= and things like that too:

var a = 65535
var a += 1   # Must define a first!
var a >>= 1

var b ^= 3  # Error: b is not defined

Flow Of Control

If-elif-else

Oneline(Ternary expression)：

if true then 1  # else null
if null then 0 else 1   # Ternary expression
if false then 1 elif 0 then 2 elif null then 3 else 4

Multi-line:

if 1 then
    print("1 is true")
end

if 0 then
    print("0 is true")
else
    print("0 is false")
end

if 0 then
    print("0 is true")
elif 1 then
    print("0 is false and 1 is true")
else
    print("0 and 1 are false")
end

While-else

Oneline (List comprehension and you cannot use else):

var a = 0
var arr = while a < 10 var a += 1
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

And multi-line:

var a = 0
while a < 10 then
    print(a)
    var a += 1
end

Else statement is like Python.

It refers to the code to be executed after the normal end of the loop, that is, if the loop is terminated by the break, the indented code under else will not be executed.

var a = 0
while a < 10 then
    print(a)
    var a += 1
    if a > 5 then break
else
    print("Else")  # will not be executed
end

You can use break and continue like other high-level programming languages:

var a = -1
while a < 10 then
    var a += 1
    if a % 2 == 0 then continue
    if a > 7 then break
    print(a)
end

This is equivalent to:

var a = -1
while a < 10 then
    var a += 1
    if a % 2 == 0 then 
        continue
    end
    if a > 7 then 
        break
    end
    print(a)
end

For-else

It's like while-else expr.

Usage:

for i = start_value(default is 0) to end_value step step_value(default is 1) then
    ...
end

Like this in Python:

for i in range(start_value, end_value, step_value):
    ...

Oneline:

var arr = for i to 5 then i ** 2  # [0, 1, 4, 9, 16]

If you want to traverse a list, you can write like this:

var arr = [1, 2, 9, 3, 15, -6, 28, 1, 7]
for i to len(arr) then
    print(arr[i])
end

And an example (use else) is as follows:

var sentence = ['an', 'apple', 'a', 'day']
for i to len(sentence) then
    if arr[i] == 'banana' then break
else
    print('No bananas!')

Try-catch-else-finally

If you want to catch errors, you can:

try 
    1 / 0
catch error, details then
    ...
end

Oneline (An expression):

try 1 / 0 catch error, details then error + ':' + details

And multi-line:

try 
    1 / 0
catch error, details then
    ...
else
    ...
finally
    ...
end

This likes Python.

Include

The keyword include is like c:

include "math.kst"

Or you can:

include "math"

It can import from /KittenScript/src/interpreter/lib or CWD.

Using KittenScript to write modules is easy. You just need write a KittenScript program and include it:

# target.kst
var pi = 3.1416
var e = 2.71828

# main.kst
include "target.kst"
print(pi, e)

And you can use Python3 too. But it's difficult. (Even you can use c or c++!)

Functions

Use function or lambda.
Default parameters and variable length parameters are temporarily not supported.

Oneline:

function max(a, b) do if a >= b then a else b
var max = lambda a, b do if a >= b then a else b

Multi-line:

function fib(n)
    if n == 1 then return 1
    if n == 2 then return 1
    return fib(n - 1) + fib(n - 2)
end

return is same as all high-level programming languages.

Namespace

You can use namespace keyword to create a namespace.

This is from heap.kst from STL:

namespace Heap
    function empty(arr) do len(arr) == 0

    function top(arr)
        if Heap.empty(arr) then throw "MathError", "empty heap"
        return arr[0]
    end

    function siftup(arr, e, last)
        var i = last
        var j = (last - 1) // 2
        while i > 0 and e < arr[j] then
            setitem(arr, i, arr[j])
            var i = j
            var j = (j - 1) // 2
        end
        setitem(arr, i, e)
    end

    function push(arr, e)
        append(arr, null)
        Heap.siftup(arr, e, len(arr) - 1)
    end

    function siftdown(arr, e, begin, end_)
        var i = begin
        var j = begin * 2 + 1
        while j < end_ then
            if j + 1 < end_ and arr[j + 1] < arr[j] then var j = j + 1
            if e < arr[j] then break
            setitem(arr, i, arr[j])
            var i = j
            var j = 2 * j + 1
        end
        setitem(arr, i, e)
    end

    function pop(arr)
        if Heap.empty(arr) then throw "MathError", "empty heap"
        var e0 = arr[0]
        var e = poplist(arr)
        if len(arr) > 0 then Heap.siftdown(arr, e, 0, len(arr))
        return e0
    end

    function heapify(arr)
        var end_ = len(arr)
        for i = end_ // 2 - 1 to -1 step -1 then
            Heap.siftdown(arr, arr[i], i, end_)
        end
    end
end

using Heap.*

You can use using to use the function.

using Heap.heapify   # Only use heapify
using Heap.*  # All

Some Examples

Fibonacci

function fib(n)
    if n == 1 then return 1
    if n == 2 then return 1
    return fib(n - 1) + fib(n - 2)
end
print(fib(15))

Quick Sort

function _partition(arr, left, right, cmp)
    var tmp = arr[left]
    while left < right then
        while left < right and cmp(tmp, arr[right]) then
            var right = right - 1
        end
        setitem(arr, left, arr[right])
        while left < right and cmp(arr[left], tmp) then
            var left = left + 1
        end
        setitem(arr, right, arr[left])
    end    
    setitem(arr, left, tmp)
    return left
end

function _quick_sort(arr, left, right, cmp)
    var mid = _partition(arr, left, right, cmp)
    _quick_sort(arr, left, mid - 1, cmp)
    _quick_sort(arr, mid + 1, right, cmp)
end

function qsort(array, cmp) do _quick_sort(array, 0, len(array) - 1, cmp)  # Quick Sort

Floor Div

function floor(dividend, divisor)
    if divisor == 0 then throw "MathError", "division by zero"

    var rev = false
    if dividend > 0 then
        var dividend = -dividend
  	    var rev = not rev
    end
    if divisor > 0 then
        var divisor = -divisor
        var rev = not rev
    end
    var candidates = [divisor]
    
    while candidates[-1] >= dividend - candidates[-1] then
        append(candidates, candidates[-1] + candidates[-1])
    end
    
    var ans = 0
    for i = len(candidates) - 1 to -1 step -1 then
        if candidates[i] >= dividend then
            var ans = ans + (1 << i)
            var dividend = dividend - candidates[i]
        end
    end
    
    return if rev then -ans else ans
end