Data types in Indie

This section is an overview of core data types of the Indie language.

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Basic data types

They are:

• float — type of double precision (64-bit) floating point numbers
• int — integer numbers
• bool — boolean values True or False
• str — string data type

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indie.Optional[T] class

In Indie (unlike in Python) it is not allowed to assign None value to a variable of any arbitrary type (e.g. basic data types). But it is allowed to do so with the help of indie.Optional[T] class.

indie.Optional[T] is similar to Python’s typing.Optional[T] with a few significant differences:

• None can be assigned to values which have indie.Optional[T] type only. None cannot be assigned to values of some T type which is not an optional type
• to write some value to an optional variable just simple assignment operator should be used
• to access T value which is stored in indie.Optional[T] it is required to explicitly call value() or value_or() method
• if value() method is called on an optional variable which is None it raises runtime error
• to test if optional variable has some value stored inside is None and is not None constructs should be used
• if variable was declared as indie.Optional[T] then T cannot be changed for that variable to some other type U

For example this will not work in Indie:

a = None  # compilation error
# ...
a = 42

Indie compiler cannot infer T type for a in this example. Yes, it may guess that a is of indie.Optional type, but it is unclear how to guess that T will be an int for it.

This will not work too:

a: int = None  # compilation error
# ...
a = 42

In this case, well, it is explicitly declared that a is not an optional type, so None cannot be assigned to it.

That is why type of a must be declared explicitly as an optional type:

a: indie.Optional[int] = None
a = 42
# ...
a = 'foobar'  # compilation error

Once variable a was declared as optional of int value, it cannot at some point start to store str values.

By the way if you do not assign any value to an optional variable it will be None too:

a: indie.Optional[int] = None
b: indie.Optional[int]

Both a and b in this example are None.

To check if optional variable a is None or not we use:

if a is None:
    # ...
if a is not None:
    # ...

To access value stored in optional variable a, the value() method should be explicitly called:

if a is not None:
    b = a.value()

If an optional variable has no value stored inside then value() method call raises a runtime error. For example:

s: indie.Optional[str]
t = s.value()  # runtime error, because `s is None == True`

But this works fine:

s: indie.Optional[str] = 'foobar'
t = s.value()

because in this case string 'foobar' is stored in optional variable s.

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Built-in container types

At the moment (Indie v4) only list[T] is implemented in the Indie language. There are partial support of a tuple[T]. It is planned to add support for dict[K, V] and set[T] in the near future.

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Series data types

• indie.Series[T] and an alias indie.SeriesF for indie.Series[float]
• indie.MutSeries[T] and an alias indie.MutSeriesF for indie.MutSeries[float]

Series[T] is a read-only container which stores series of T values. MutSeries[T] extends Series[T] with only __setitem__ method, which allows writing to the last element of the container (which syntactically looks like some_mut_series[0] = some_value).

Type T can be (almost) any type in Indie, not just float, but also int, bool, str, etc.

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Context data types

There are three context classes:

• indie.Context is a base class that represents a context of a chart instrument
• indie.MainContext is a class that represents main context, extends indie.Context
• indie.SecContext is a class that represents secondary context, extends indie.Context

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Algorithm base class

There is a indie.Algorithm base class. All algorithms from indie.algorithms package are inherited from it.