7.6. Vectors

Vectors are arrays that can contain any of the following base types:

boolean
integer
real
character

In Gazprea the number of elements in the vector also determine its type. A 3 element vector of any base type is always considered a different type from a 2 element vector.

7.6.1. Declaration

Aside from any type specifiers, the element type of the vector is the first portion of the declaration. A vector is then declared using square brackets immediately after the element type.

If possible, initialization expressions may go through an implicit type conversion. For instance, when declaring a real vector if it is initialized with an integer value the integer will be promoted to a real value, and then used as a scalar initialization of the vector.

Explicit Size Declarations

When a vector is declared it may be explicitly given a size. This size can be given as any integer expression, thus the size of the vector may not be known until runtime.
```
<type>[<int-expr>] <identifier>;
<type>[<int-expr>] <identifier> = <type-expr>;
<type>[<int-expr>] <identifier> = <type-vector>;
```
The size of the vector is given by the integer expression between the square brackets.

If the vector is given a scalar value (type-expr) of the same element type then the scalar value is duplicated for every single element of the vector.

A vector may also be initialized with another vector. If the vector is initialized using a vector that is too small then the vector will be null padded. However, if the vector is initialized with a vector that is too large then a SizeError should be thrown at compile-time or run-time. Check the Compile-time vs Run-time Size Errors section to know when you should throw the error.
Inferred Size Declarations

If a vector is assigned an initial value when it is declared, then its size may be inferred. There is no need to repeat the size in the declaration because the size of the vector on the right-hand side is known.
```
<type>[*] <identifier> = <type-vector>;
```
Inferred Type and Size

It is also possible to declare a vector with an implied type and length using the var or const keyword. This type of declaration can only be used when the variable is initialized in the declaration, otherwise the compiler will not be able to infer the type or the size of the vector.
```
integer[*] v = [1, 2, 3];
var w = v + 1;
```
In this example the compiler can infer both the size and the type of w from v. The size may not always be known at compile time, so this may need to be handled during runtime.

7.6.2. Null

Vector of null elements.

When initializing a vector to a value of null an explicit size must be given. Such initialization is equivalent to promoting a null value of the element type to the vector.

7.6.3. Identity

Vector of identity elements.

When initializing a vector to a value of identity an explicit size must be given. Such initialization is equivalent to promoting a identity value of the element type to the vector.

7.6.4. Construction

A vector value in Gazprea may be constructed using the following notation:

[expr1, expr2, ..., exprN]

Each expK is an expression with a compatible type. In the simplest cases each expression is of the same type, but it is possible to mix the types as long as all of the types can be promoted to a common type. For instance it is possible to mix integers and real numbers.

real[*] v = [1, 3.3, 5 * 3.4];

It is also possible to construct a single-element vector using this method of construction.

real[*] v = [7];

Gazprea DOES support empty vectors.

real[*] v = []; /* Should create an empty vector */

7.6.5. Operations

Vector Operations and functions
1. length
  
  The number of elements in a vector is given by the built-in functions length. For instance:
```
integer[*] v = [8, 9, 6];
integer numElements = length(v);
```
  In this case numElements would be 3, since the vector v contains 3 elements.
2. Concatenation
  
  Two vectors with the same element type may be concatenated into a single vector using the concatenation operator, ||. For instance:
```
[1, 2, 3] || [4, 5] // produces [1, 2, 3, 4, 5]
[1, 2] || [] || [3, 4] // produces [1, 2, 3, 4]
```
  Concatenation is also allowed between vectors of different element types, as long as one element type is coerced automatically to the other. For instance:
```
integer[3] v = [1, 2, 3];
real[3] u = [4.0, 5.0, 6.0];
real[6] j = v || u;
```
  would be permitted, and the integer vector v would be promoted to a real vector before the concatenation.
  
  Concatenation may also be used with scalar values. In this case the scalar values are treated as though they were single element vectors.
```
[1, 2, 3] || 4 // produces [1, 2, 3, 4]
1 || [2, 3, 4] // produces [1, 2, 3, 4]
```
3. Dot Product
  
  Two vectors with the same size and a numeric element type(types with the +, and \* operator) may be used in a dot product operation. For instance:
```
integer[3] v = [1, 2, 3];
integer[3] u = [4, 5, 6];

/* v[1] * u[1] + v[2] * u[2] + v[3] * u[3] */
/* 1 * 4 + 2 * 5 + 3 * 6 &=&  32 */
integer dot = v ** u;  /* Perform a dot product */
```
4. Range
  
  The .. operator creates an integer vector holding the specified range of integer values. This operator must have an expression resulting in an integer on both sides of it. These integers mark the inclusive upper and lower bounds of the range.
  
  For example:
```
1..10 -> std_output;
(10-8)..(9+2) -> std_output;
```
  prints the following:
```
[1 2 3 4 5 6 7 8 9 10]
[2 3 4 5 6 7 8 9 10 11]
```
  The number of integers in a range may not be known at compile time when the integer expressions use variables. In another example, assuming at runtime that i is computed as -4:
```
i..5 -> std_output;
```
  prints the following:
```
[-4 -3 -2 -1 0 1 2 3 4 5]
```
  Therefore, it is valid to have bounds that will produce an empty vector because the difference between them is negative.
1. Indexing
  
  A vector may be indexed in order to retrieve the values stored in the vector. A vector may be indexed using integers. Gazprea is 1-indexed, so the first element of a vector is at index 1 (as opposed to index 0 in languages like C). For instance:
```
integer[3] v = [4, 5, 6];
integer x = v[2]; /* x == 5 */
integer y = [4,5,6][3] /* y == 6 */
```
  Out of bounds indexing should cause an error.
2. Stride
  
  The by operator is used to specify a step-size greater than 1 when indexing across a vector. It produces a new vector with the values indexed by the given stride. For instance:
```
integer[*] v = 1..5 by 1; /* [1, 2, 3, 4, 5] */
integer[*] u = v by 1; /* [1, 2, 3, 4, 5] */
integer[*] w = v by 2; /* [1, 3, 5] */
integer[*] l = v by 3; /* [1, 4] */
```
Operations of the Element Type

Unary operations that are valid for the Element type of a vector may be applied to the vector in order to produce a vector whose result is the equivalent to applying that unary operation to each element of the vector. For instance:
```
boolean[*] v = [true, false, true, true];
boolean[*] nv = not v;
```
nv would have a value of [not true, not false, not true, not true] = [false, true, false, false].

Similarly most binary operations that are valid to the element type of a vector may be also applied to two vectors. When applied to two vectors of the same size, the result of the binary operation is a vector formed by the element-wise application of the binary operation to the vector operands.
```
[1, 2, 3, 4] + [2, 2, 2, 2] // results in [3, 4, 5, 6]
```
Attempting to perform a binary operation between two vectors of different sizes should result in a SizeError.

When one of the operands of a binary operation is a vector and the other operand this a scalar value, then the scalar value must first be promoted with a vector of the same size as the vector operand and with the value of each element equal the scalar value. For example:
```
[1, 2, 3, 4] + 2 // results in [3, 4, 5, 6]
```
Additionally the element types of vectors may be promoted, for instance in this case the integer vector must be promoted to a real vector in order to perform the operation:
```
[1, 2, 3, 4] + 2.3 // results in [3.3, 4.3, 5.3, 6.3]
```
The equality operation is the exception to the behavior of the binary operations. Instead of producing a boolean vector, an equality operation checks whether or not all of the elements of two vectors are equal, and return a single boolean value reflecting the result of this comparison.
```
[1, 2, 3] == [1, 2, 3]
```
yields true
```
[1, 1, 3] == [1, 2, 3]
```
yields false

The != operation also produces a boolean instead of a boolean vector. The result is the logical negation of the result of the == operator.

7.6.6. Type Casting and Type Promotion

To see the types that vector may be cast and/or promoted to, see the sections on Type Casting and Type Promotion respectively.