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Beau­tiful Racket / racket school 2019

Day 3

Mission

Imple­ment these language features:

  1. decimal numbers

    123.456;
    -.123;
    42.;
    123.456;
-.123;
42.;
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  2. strings (either single- or double-quoted). Naive handling is OK (= you can assume that the strings don’t contain escaped quote marks. There aren’t any strings like that in the test program.)

    "please";
    "don't";
    'say "hello"';
    'world';
    "please";
"don't";
'say "hello"';
'world';
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  3. vari­able defin­tion with var. Vari­able names can be any sequence of alphanu­meric char­ac­ters that does not contain reserved tokens and that does not repre­sent a number. Thus, a42 is a valid vari­able name, but a;42 and 42 are not.

    var 4aa = -.123;
    var b3b = "foo";
    var 1bßc = 0.;
    var d7 = 'bar';
    4aa; b3b; 1bßc; d7;
    var 4aa = -.123;
var b3b = "foo";
var 1bßc = 0.;
var d7 = 'bar';
4aa; b3b; 1bßc; d7;
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Optional

  1. What happens when you hover your cursor over the vari­able names in DrRacket? What makes this behavior possible?

  2. Imple­ment multiple vari­able assign­ment.

    var a = b = 25;
    a; // 25
    b; // 25
    var a = b = 25;
a; // 25
b; // 25
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  3. Imple­ment all of the string-lexing rules of #lang racket.

    Hint: You’ll want to imple­ment them all at once, not one at a time.

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