=: (Is (Global)) Noun/Other
Is (Global or Local), also called Copula, changes the value of a given target.
A sentence using Copula =: is always of the form: target =: value.
Likewise a sentence using Copula =. is always of the form: target =. value.
The target can be any valid J identifier, or an expression which evaluates to a boxed or unboxed list of one or more valid J identifiers.
'fe fi'=: 100+ 0 1 NB. the target is a string representing two J words ]fo=: fe+fi NB. the target is a J word: fo, the value is a noun expression 201 fe ; fi ; fo +---+---+---+ |100|101|201| +---+---+---+ fum=: 1&+ NB. the target is a J word: fum, the value is a tacit verb definition ]fo=: fum fo NB. the value is an expression in the verb: fum, it changes the J word: fo 202
The target can also be an expression which evaluates to the required J word(s). Putting parentheses around the target ensures that it is evaluated before the Copula is applied.
aa=: 'a' , ": NB. aa is a verb which creates a suffixed J word: 'a*' aa each 1 2 NB. Two such J words, suffixed: '1' and '2' +--+--+ |a1|a2| +--+--+ (aa each 1 2)=: 200+ i.2 NB. creates scalar nouns of the above J words a1 ; a2 +---+---+ |200|201| +---+---+
Used to create nouns, adverbs, conjunctions and verbs, the building-blocks of an application.