# jats-ug/ATS_Foundations

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# Basic data types

In the chapter, we learn some basic datatypes on ATS.

## Integer

First, let's create a text file named print_int.dats has following context:

.. literalinclude:: code/basic_datatype/print_int.dats
:language: ocaml
:linenos:



This program prints integer 3 on console. Then compile it.

.. literalinclude:: code/basic_datatype/print_int_compile.txt
:language: shell



You get the result just as our intended. The 3 in the print_int.dats file is a literal, and type of the value is int.

It's available doing basic arithmetic operations on integers. Addition operator is +, subtraction is - and multiplication is *. let's create a text file named int_op.dats has following context:

.. literalinclude:: code/basic_datatype/int_op.dats
:language: ocaml
:linenos:



The int_op.dats file includes share/atspre_staload.hats file that is needed to use ATS's template. Some operators such like + are implemented using the template on ATS language implementation.

You will get following intended result, by compiling the code and running it.

.. literalinclude:: code/basic_datatype/int_op_compile.txt
:language: shell



Multiplication and division are given priority over addition and subtraction, without parentheses.

You can also do division / and modulus %.

.. literalinclude:: code/basic_datatype/divmod_op.dats
:language: ocaml
:linenos:



Let's compile and run it.

.. literalinclude:: code/basic_datatype/divmod_op_compile.txt
:language: shell



By the way, what happen if you do division with 0 as divisor on a new code divzero.dats?

.. literalinclude:: code/basic_datatype/divzero.dats
:language: ocaml
:linenos:



Interestingly, divzero.dats occurs an error on compiling time, even though many programming language take care division with 0 as run-time error.

.. literalinclude:: code/basic_datatype/divzero_compile.txt
:language: shell



However, the compilation error message is hard to understand for the reader on this chapter. I'll explain detail of the error messages elsewhere.

Note

Exercise: Calculate following expressions on ATS language.

1. 7 - 3 \times 4
2. 7 \div 2 \times 2
3. 7 \times 2 \div 2

## Real number

Literal of real number is represented using a decimal point, and the type is double.

.. literalinclude:: code/basic_datatype/print_double.dats
:language: ocaml
:linenos:



A value of real number is able to be printed using println!.

.. literalinclude:: code/basic_datatype/print_double_compile.txt
:language: shell



Addition operator +, subtraction -, multiplication * and division / can be used on real number. Please see following double_op.dats:

.. literalinclude:: code/basic_datatype/double_op.dats
:language: ocaml
:linenos:


.. literalinclude:: code/basic_datatype/double_op_compile.txt
:language: shell



Zeros after the decimal point are optional.

.. literalinclude:: code/basic_datatype/double_op_nozero.dats
:language: ocaml
:linenos:



ATS is different to OCaml, and can use operators between different types (such like int and double).

.. literalinclude:: code/basic_datatype/double_int_op.dats
:language: ocaml
:linenos:


.. literalinclude:: code/basic_datatype/double_int_op_compile.txt
:language: shell



This mixing is based on ATS template system.

Note

Exercise: Calculate following expressions on ATS language.

1. 2 \times 3.14 \times 10
2. 1.73 \times 1.73
3. 7 / 2

## Boolean value

Boolean value is a value for true or false. On ATS language, true is for true and false for false. Type of the boolean value is bool.

.. literalinclude:: code/basic_datatype/print_bool.dats
:language: ocaml
:linenos:


.. literalinclude:: code/basic_datatype/print_bool_compile.txt
:language: shell



We can use logical operations on the boolean value.x && is for "and", || for "or" and not for "negation", in the order of descending priorities.

.. literalinclude:: code/basic_datatype/bool_op.dats
:language: ocaml
:linenos:


.. literalinclude:: code/basic_datatype/bool_op_compile.txt
:language: shell



true and false are rarely used on real programming. Normally, we use them to test whether some conditions hold. Examples of the test operators are: = is for "equality", != for "inequality", > for "greater than", < for "less than", >= for "greater than or equal", and <= "less than or equal".

.. literalinclude:: code/basic_datatype/bool_test.dats
:language: ocaml
:linenos:


.. literalinclude:: code/basic_datatype/bool_test_compile.txt
:language: shell



Note

Exercise: Test conditions of following sentences on ATS language.

1. "2 is greater than 3."
2. "The second power of 3.1415 is not less than 10."
3. "The remainder obtained by dividing 8 by 3 is equal to 2."
4. "3 + 4 + 5 is equal to 4 \times 3."

## The other data types

Character string and the other data types are explained later.