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Beau­tiful Racket / racket school 2019

Day 3

Mission

Imple­ment these language features:

  1. func­tion expres­sions with function, with any number of argu­ments

    var dbl = function(x) { x + x; };
    var prod = function(x, y) { x * y; };
    1
2
    var dbl = function(x) { x + x; };
var prod = function(x, y) { x * y; };
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  2. func­tion appli­ca­tion, with any expres­sion as a valid argu­ment

    var dbl = function(x) { x + x; };
    var prod = function(x, y) { x * y; };
    dbl(42); // 84
    dbl(42 - 40); // 4
    prod(42, 50); // 2100
    1
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    var dbl = function(x) { x + x; };
var prod = function(x, y) { x * y; };
dbl(42); // 84
dbl(42 - 40); // 4
prod(42, 50); // 2100
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    Hint: Func­tion expres­sions and func­tion appli­ca­tion also require handling of state­ment blocks between curly braces.

  3. Upgrade + to handle string concate­na­tion. Numbers “added” to strings should be converted to a string repre­sen­ta­tion. Exact inte­gers should not have a trailing .0.

    var a = 24.5;
    var b = "foo";
    a + a + b; // 49foo
    a + b + a; // 24.5foo24.5
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    var a = 24.5;
var b = "foo";
a + a + b; // 49foo
a + b + a; // 24.5foo24.5
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  4. alert func­tion that prints its argu­ments as text with an ALERT! prefix.

    alert(21 + 21 + "hello"); // ALERT! 42hello
    1
    alert(21 + 21 + "hello"); // ALERT! 42hello
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Optional

  1. Imple­ment the usual function defi­n­i­tion short­hand, with the func­tion name on the inside.

    function dbl(x) { x + x; };
    function prod(x, y) { x * y; };
    1
2
    function dbl(x) { x + x; };
function prod(x, y) { x * y; };
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  2. Make alert pop up an actual dialog box in the GUI with the message.

    Hint: Adapt this sample code in the docs.

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