Editing JOSS (section)

===Ranges===
Another advanced feature of JOSS was that it had the concept of a [[Range (computer programming)|range]] as a built-in type that could be stored and manipulated. Ranges are normally found as the inputs to [[for loop]]s, where they are part of the syntax of the loop itself. For instance, in BASIC one writes a for loop using this basic syntax:
{{sxhl|2=basic|1=
 FOR I=1 TO 5 STEP 2
}}
This will perform a loop that assigns I the values 1, 3, 5 and then exits.

JOSS used a somewhat obscure format to define the limits of the loop. The equivalent code in JOSS would be:

  I=1(2)5

Note that this code does not include a for. That is because in JOSS, ranges are first-class citizens of the language, not something that is part of a loop as in BASIC. Ranges can be defined and used in many contexts outside loops. For example, here is a conditional expression that evaluates the factorial of a parameter x:{{sfn|Gimble|1967|p=75}}

 Let f(x)=[x=0:1 ; fp(x)=0:prod(i=1(1)x:i)].

In this example, there are two main propositions, separated by the semicolon. The first, on the left, states that if the parameter x is 0, the condition should immediately return 1. If that proposition fails, it moves to the second test, on the right. This one checks if the fractional part of x is zero (i.e., it is an integer), and if so, it calls the {{code|prod}} function to multiply a range of values. The {{code|prod}}'s parameter is also a proposition, but in this case, the test is replaced by a loop iterator that runs from 1 to x stepping by 1. If that proposition is true, which is it for all values of the loop, it returns the index i. This causes a series of values to be sent into {{code|prod}} from 1 to x.{{sfn|Gimble|1967|p=75}}

The combination of these features allows for complex functions to be written in a few commands. This sort of functionality has only become common in much more modern languages, which typically use [[iterator]]s or a [[Map (higher-order function)|map function]] to provide the same outcomes. JOSS's capability to combine decisions and loops in a compact form is unknown in other languages of the era, including offshoots like FOCAL.