Lesson 14 – Using arrays in 8th – part 2

More on arrays

Now we are going to see a few more advanced words in the a (array) namespace.

Iterating over an array – the word a:each

Later we will see that 8th has special words for iterating / looping.

However, there are also words like a:each that make it very easy to use iteration under the hood, without having to bother with the details.

The SED of a:each is \ a w – a

• a = input array
• w = the helper word

The SED of show (in our example below) is \ index value --

• index = index of current array item
• value = value of current array item

So a:each is such a word, that takes another word as a parameter (as we saw in the previous lesson).

The show word will be handed the value of the item at TOS and it’s index in 2nd position on the stack.

Example

Note that we have to use swap in order to show the index before the value!

Note that 8th arrays can contain values of different types (unlike e.g. in C).

Output:

Note that a:each leaves the array on the stack after executing!

Reducing an array using a:reduce

Reducing is a process like this:

1. use an array
2. get a start value x (which will be used as an accumulator)
3. for every item in the array:
1. do something with the values of the current array element and x (and also consume them)
2. push the result on the stack; that value will then be used as the x value in the next iteration

The SED of a:reduce is \ a w x – x

• a = input array
• w = the helper word
• x = initial value, also used as an accumulator

The SED of sum (just an example word below) is \ value x -- newx

• value = value of current array item
• x = initial value, also used as the accumulator

Example

Output:

Filtering an array using a:filter

This word uses a helper word that returns either true or false.

Only if that helper word retruns true, the corresponding element will be put in an output array.

The SED of a:filter is \ a1 w – a2

• a1 = input array
• w = the helper word
• a2 = output array

The SED of iseven (just an example word below) is \ value -- boolean
• value = value of current array item
• boolean = true or false

Example

Note that the not word regards the value 0 (zero) as false! So when value 0 is encountered, not will output true and otherwise false.

Output:

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