=== Array Subscript Expressions

An *array subscript expression* is an expression that selects an element from
an array value.

==== Syntax

<<Expressions,_expression_>> `[` <<Expressions,_expression_>> `]`

==== Semantics

The following rules give the meaning of an array subscript expression
stem:[e_1] `[` stem:[e_2] `]`:

. The type of stem:[e_1] must be an <<Types_Array-Types,array type>> or
<<Types_Internal-Types_Anonymous-Array-Types,anonymous array type>>
with element type _T_ and size _n_.

. The type of stem:[e_2] must be <<Type-Checking_Type-Conversion,convertible to>>
<<Types_Internal-Types_Integer,_Integer_>>.
stem:[e_2] must
<<Evaluation,evaluate>> to a value _m_ after
<<Evaluation_Type-Conversion,conversion>> to _Integer_.
_m_ must be greater than or equal to zero and less than _n_.

. Evaluation of stem:[e_1] `[` stem:[e_2] `]` occurs as follows:

.. Evaluate stem:[e_1] to an <<Values_Array-Values,array value>> or
<<Values_Anonymous-Array-Values,anonymous array value>> _v_.

.. Evaluate stem:[e_2] to an <<Values_Integer-Values,integer value>> _m_.

.. The value of the entire expression is the value associated with index _m_ of _v_.

==== Example

[source,fpp]
----
constant a = [ 2, 4, 6 ]
constant b = a[1] # b is an integer with value 4
constant c = [ 0, 1, 2 ][1] # c is an integer with value 1
constant d = a[-1] # error, index is out of bounds (negative)
constant e = [ 0, 1, 2 ][3] # error, index is out of bounds (past end)
----