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Function

Overview

Lambda

Lambda is a simple style of an anonymous function. & is used instead of function, and => expression is used instead of block.

var calc = &(func, a, b) => func(a, b);
System.println(calc(&(a, b) => a + b, 2, 3));   // 5

Note that => { /* block */ } is also available, so you can not use &(args) => { /* object */ }. If you want to use an object, you have to write it with &(args) => ({ /* object */ }).

Block object

If the function has no arguments, a lambda can be written like &{...} style.

var a = 10;
var doit = &(block) => block();
System.println(doit(&{
    return a + 100;
}));

Function block syntax

Block style

This is not same as a block object above. A lambda can be wrapped with { and }, and it is the base of some simple syntax. For example, the above doit function can be written as below.

var doit = { &(block) => block() };

Omit the argument list

As combining with the block style and a numbered parameter, you can remove an argument list itself. For example, you can write the doit function as below.

var doit = { => _1() };

No arrow style

When the block style without an arrow of => operator, it can be just like a block statement with argument list inside block.

var add = { &(a, b)
    return a + b;
};
System.println(add(1, 2));  // => 3

If you want to omit an argument list in the normal statement, you have to use it as a block object.

var add = &{
    return _1 + _2;
};
System.println(add(1, 2));  // => 3

The last argument in function call

If the last argument in function call is a function object, that can be placed outside the argument list with a block style. For example, the 4 styles below are absolutely same.

callFunction(&(a, b) => a + b);

callFunction(&(a, b) => {
    return a + b;
});

callFunction() { &(a, b) => a + b };

callFunction() { &(a, b)
    return a + b;
};

In this case, you can omit an argument list itself without a block object style. It means you do not have to use & before a block when it is the argument written outside the argument list.

function callFunction(f) {
    System.println(f(1, 2));    // => 3
}
callFunction() {
    return _1 + _2;
};

And you can also omit the parenthesis of function call when there is no argument list except the outside argument.

function callFunction(f) {
    System.println(f(1, 2));    // => 3
}
callFunction {
    return _1 + _2;
};

Examples

Example 1. Fibonacci

Code

var fib = &(n) => {
    if (n < 3) return n;
    return fib(n-2) + fib(n-1);
};
System.println(fib(34));  // => 9227465

Result

9227465

Example 2. Factorial

Code

var fact = &(a) => {
    if (a < 1) return 1;
    return a * fact(a-1);
};
for (var i = 0; i <= 20; ++i) {
    System.println("fact(%{i}) = ", fact(i));
}
System.println("fact(500) = ", fact(500));

Result

fact(0) = 1
fact(1) = 1
fact(2) = 2
fact(3) = 6
fact(4) = 24
fact(5) = 120
fact(6) = 720
fact(7) = 5040
fact(8) = 40320
fact(9) = 362880
fact(10) = 3628800
fact(11) = 39916800
fact(12) = 479001600
fact(13) = 6227020800
fact(14) = 87178291200
fact(15) = 1307674368000
fact(16) = 20922789888000
fact(17) = 355687428096000
fact(18) = 6402373705728000
fact(19) = 121645100408832000
fact(20) = 2432902008176640000
fact(500) = 1220136825991110068701238785423046926253574342803192842192413588385845373153881997605496447502203281863013616477148203584163378722078177200480785205159329285477907571939330603772960859086270429174547882424912726344305670173270769461062802310452644218878789465754777149863494367781037644274033827365397471386477878495438489595537537990423241061271326984327745715546309977202781014561081188373709531016356324432987029563896628911658974769572087926928871281780070265174507768410719624390394322536422605234945850129918571501248706961568141625359056693423813008856249246891564126775654481886506593847951775360894005745238940335798476363944905313062323749066445048824665075946735862074637925184200459369692981022263971952597190945217823331756934581508552332820762820023402626907898342451712006207714640979456116127629145951237229913340169552363850942885592018727433795173014586357570828355780158735432768888680120399882384702151467605445407663535984174430480128938313896881639487469658817504506926365338175055478128640000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Example 3. While Loop

Code

var n = 10000;
var loop_while = &(n) => {
    var v = 0, i = 0;
    while (i <= n) {
        v += i++;
    }
    return v;
};
System.println("while(%{n}) = ", loop_while(n));

Result

while(10000) = 50005000

Example 4. For Loop

Code

var n = 10000;
var loop_for = &(n) => {
    var v = 0;
    for (var i = 0; i <= n; ++i) {
        v += i;
    }
    return v;
};
System.println("for(%{n}) = ", loop_for(n));

Result

for(10000) = 50005000

Example 5. Do-While Loop

Code

var n = 10000;
var loop_do_while = &(n) => {
    var v = 0, i = 0;
    do {
        v += i++;
    } while (i <= n);
    return v;
};
System.println("do_while(%{n}) = ", loop_do_while(n));

Result

do_while(10000) = 50005000

Example 6. Evaluation with double

Code

var b = 1.7;
var test = &(a:dbl) => {
    return a + b;
};
System.println(test(1.5));

Result

3.2

Example 7. Label to While

Code

var n = 10000;
var loop_while = &(n) => {
    var v = 0, i = 0;
    LABEL::
    while (1) {
        while (i <= n) {
            if (i == 9) {
                ++i;
                continue;
            }
            v += i++;
            if (i > 10) break LABEL;
        }
    }
    return v;
};
System.println("while(%{n}) = ", loop_while(n));

Result

while(10000) = 46

Example 8. Label to For

Code

var n = 10000;
var loop_for = &(n) => {
    var v = 0;
    LABEL::
    while (1) {
        for (var i = 0; i <= n; ++i) {
            if (i == 9) continue;
            v += i;
            if (i == 10) break LABEL;
        }
    }
    return v;
};
System.println("for(%{n}) = ", loop_for(n));

Result

for(10000) = 46

Example 9. Label to Do-While

Code

var n = 10000;
var loop_do_while = &(n) => {
    var v = 0, i = 0;
    LABEL::
    while (1) {
        do {
            if (i == 9) {
                ++i;
                continue;
            }
            v += i++;
            if (i > 10) break LABEL;
        } while (i <= n);
    }
    return v;
};
System.println("do_while(%{n}) = ", loop_do_while(n));

Result

do_while(10000) = 46

Example 10. Try-Catch-Finally

Code

var b = 100;
var c = 100;
function test() {
    var d = 0;
    return function (n) {
        var a = 100;
        try {
            try {
                a /= d;
            } finally {
                ++b;
            }
            b %= 9;
        } catch (e) {
            c = 999;
            throw;
        } finally {
            ++b;
        }
        return a;
    };
};

var try_catch = test();
try {
    System.println("b = ", b);
    System.println(try_catch(10));
} catch (e) {
    System.println(e.what());
    e.printStackTrace();
} finally {
    System.println("b = ", b);
    System.println("c = ", c);
}

Result

b = 100
Divide by zero
Stack Trace Information:
        at <main-block>(test.kx:27)
b = 102
c = 999

Example 11. Block style (1)

Code

function calc(x, y, func) {
    return func(x, y);
}

// The callback function can be put outside an arugument list.
System.println("add = " + calc(10, 2) { &(a, b) => a + b });
System.println("sub = " + calc(10, 2) { &(a, b) => a - b });
System.println("mul = " + calc(10, 2) { &(a, b) => a * b });
System.println("div = " + calc(10, 2) { &(a, b) => a / b });
System.println("add = " + calc(10, 2) { &() => _1 + _2 });
System.println("sub = " + calc(10, 2) { &() => _1 - _2 });
System.println("mul = " + calc(10, 2) { &() => _1 * _2 });
System.println("div = " + calc(10, 2) { &() => _1 / _2 });

System.println("add = " + calc(10, 2) { => _1 + _2 });
System.println("sub = " + calc(10, 2) { => _1 - _2 });
System.println("mul = " + calc(10, 2) { => _1 * _2 });
System.println("div = " + calc(10, 2) { => _1 / _2 });

Result

add = 12
sub = 8
mul = 20
div = 5
add = 12
sub = 8
mul = 20
div = 5
add = 12
sub = 8
mul = 20
div = 5

Example 12. Block style (2)

Code

var r = [1, 2, 3].map() {
    return _1 * 2;
};
System.println(r);  // => [2, 4, 6]

Result

[2, 4, 6]

Example 13. Block style (3)

Code

var r = [1, 2, 3].map {
    return _1 * 2;
};
System.println(r);  // => [2, 4, 6]

Result

[2, 4, 6]

Example 14. Block style (4)

Code

r = (1..10).sort { => _2 <=> _1 };
System.println(r);  // => [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

Result

[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]