Chapter 5. Основы GEL
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# Chapter 5. Основы GEL

GEL stands for Genius Extension Language. It is the language you use to write programs in Genius. A program in GEL is simply an expression that evaluates to a number, a matrix, or another object in GEL. Genius Mathematics Tool can be used as a simple calculator, or as a powerful theoretical research tool. The syntax is meant to have as shallow of a learning curve as possible, especially for use as a calculator.

## Значения

Values in GEL can be numbers, Booleans, or strings. GEL also treats matrices as values. Values can be used in calculations, assigned to variables and returned from functions, among other uses.

### Числа

Integers are the first type of number in GEL. Integers are written in the normal way.

    1234

Hexadecimal and octal numbers can be written using C notation. For example:

    0x123ABC
    01234

Or you can type numbers in an arbitrary base using `<base>\<number>`. Digits higher than 10 use letters in a similar way to hexadecimal. For example, a number in base 23 could be written:

    23\1234ABCD

The second type of GEL number is rationals. Rationals are simply achieved by dividing two integers. So one could write:

    3/4

to get three quarters. Rationals also accept mixed fraction notation. So in order to get one and three tenths you could write:

    1 3/10

The next type of number is floating point. These are entered in a similar fashion to C notation. You can use `E`, `e` or `@` as the exponent delimiter. Note that using the exponent delimiter gives a float even if there is no decimal point in the number. Examples:

    1.315
    7.887e77
    7.887e-77
    .3
    0.3
    77e5

When Genius prints a floating point number it will always append a `.0` even if the number is whole. This is to indicate that floating point numbers are taken as imprecise quantities. When a number is written in the scientific notation, it is always a floating point number and thus Genius does not print the `.0`.

The final type of number in GEL is the complex numbers. You can enter a complex number as a sum of real and imaginary parts. To add an imaginary part, append an `i`. Here are examples of entering complex numbers:

    1+2i
    8.01i
    77*e^(1.3i)

### Important

При вводе мнимых чисел перед символом `i` должно стоять число. Если использовать символ `i` сам по себе, Genius интерпретирует его как ссылку на переменную `i`. Если нужно указать саму мнимую единицу `i`, используйте вместо неё `1i`.

Чтобы использовать смешанные дроби в мнимых числах, нужно взять смешанную дробь в круглые скобки: (например, `(1 2/5)i`)

### Логические значения

Genius также поддерживает логические значения. Определены две логические константы: `true` и `false`; их можно использовать, как и любую переменную. В качестве псевдонимов к ним можно также использовать `True`, `TRUE`, `False` и `FALSE`.

Там, где требуется логическое выражение, можно использовать логическое значение или любое выражение, дающее в результате число или логическое значение. Если Genius нужно использовать число как логическое значение, он будет интерпретировать 0 как `false` и любое другое число как `true`.

In addition, you can do arithmetic with Boolean values. For example:

    ( (1 + true) - false ) * true

is the same as:

    ( (true or true) or not false ) and true

Only addition, subtraction and multiplication are supported. If you mix numbers with Booleans in an expression then the numbers are converted to Booleans as described above. This means that, for example:

    1 == true

always evaluates to `true` since 1 will be converted to `true` before being compared to `true`.

### Строки

Like numbers and Booleans, strings in GEL can be stored as values inside variables and passed to functions. You can also concatenate a string with another value using the plus operator. For example:

    a=2+3;"The result is: "+a

will create the string:

    The result is: 5

You can also use C-like escape sequences such as `\n`,`\t`,`\b`,`\a` and `\r`. To get a `\` or `"` into the string you can quote it with a `\`. For example:

    "Slash: \\ Quotes: \" Tabs: \t1\t2\t3"

will make a string:

    Slash: \ Quotes: " Tabs: 	1	2	3

Do note however that when a string is returned from a function, escapes are quoted, so that the output can be used as input. If you wish to print the string as it is (without escapes), use the `print` or `printn` functions.

In addition, you can use the library function `string` to convert anything to a string. For example:

    string(22)

will return

    "22"

Strings can also be compared with `==` (equal), `!=` (not equal) and `<=>` (comparison) operators

### Null

There is a special value called `null`. No operations can be performed on it, and nothing is printed when it is returned. Therefore, `null` is useful when you do not want output from an expression. The value `null` can be obtained as an expression when you type `.`, the constant `null` or nothing. By nothing we mean that if you end an expression with a separator `;`, it is equivalent to ending it with a separator followed by a `null`.

Example:

    x=5;.
    x=5;

Некоторые функции возвращают `null`, если невозможно вернуть значение или произошла ошибка. Также `null` используется как пустой вектор или матрица, или пустая ссылка.

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