5. Generator

A generator creates a series of numbers by applying an expression to the value of an index. A generator is similar to a C style for loop. For this assignment, the index variable will always start at the lower bound and continue until it is equal to the upper bound (the last value of the index will be the upper bound). The index will always be incremented by the integer value 1. In C, this would be:

for(int i = <start>; i <= <end>; ++i)

5.1. Generator Format

A generator statement will always follow the same format:

[<id> in <int_1>..<int_2> | <expr>];

  • id is the identifier of the generator’s index.

  • int_1 is an integer representing the lower bound of the generator

  • int_2 is an integer representing the upper bound of the generator

  • expr is an expression

Assertion: int_1 and int_2 will never be expressions, only integer literals. (simple-bounds)
Assertion: int_1 will be never be greater than int_2. (sane-bounds)
Assertion: If an identifier is used in expr then it will match id. (matching-id)

For this assignment the value of the identifier variable <id>:

  1. is initialized to the value of int_1.

  2. is used to evaluate the expression.

  3. is incremented by one.

  4. stops when its value is greater than int_2.

For each value assumed by id, expr is used to generated the next number in the series.

Examples of valid generators:

[i in 1..10 | i * i];
[i in 0..10 | 2 ^ i];

In this assignment white space is not important so the following is valid:

[i
in
1
..
10
|
i*i];
[i in 1..10|2^i];

Assertion: Whitespace is guaranteed to be a space, a tab, a carriage return, or a new line. (simple-whitespace)

Because identifiers need white space to separate each other the following is invalid:

[iin1..10|i*i];
[i in1..10|2^i];