Editing JOSS (section)

===Expressions and propositions===
A unique feature of JOSS was its handling of logical expressions. Most computer languages offer some way to form a multi-part mathematical expression, for instance, {{code|Set x{{=}}(1+2)·3.}} which sets the variable x to the value 9. JOSS expanded on this concept by clearly defining the concept of the "proposition", an expression that returns a logical value, true or false, instead of a numeric one. They were mostly seen in {{code|If}} statements, as in the examples above, but the Boolean value could also be stored in a variable directly,{{sfn|Gimble|1967|p=77}} or one could convert true to 1 and false to 0 using the {{code|tv}} (truth value) function.{{sfn|Gimble|1967|p=24, 69}}

In addition to propositions, JOSS also had the concept of "conditional expressions". These consisted of strings of propositions along with code that would run if that proposition was true. This allowed multi-step decision trees to be written in a single line. They serve a purpose similar to the [[?:|ternary operator]] found in modern languages like [[C programming language|C]] or [[Java programming language|Java]], where they are used to return a value from a compact structure implementing [[if-then-else]]. JOSS' version has any number of conditionals, not just three, so it is more of a compact [[switch statement]] than a compact if-then.{{sfn|Gimble|1967|p=75}}

This example recreates the function of the {{code|sgn}} function:{{sfn|Marks|1971|p=41}}

 Let s(x)=[x=0:0; x>0:1; x<0:-1].

This defines a function "s" which takes a single parameter, "x", and makes three consecutive tests against it. Whichever test succeeds first returns the corresponding value after the colon.{{sfn|Gimble|1967|p=25}}