A function definition operator
Kenneth E. Iverson, Peter K. Wooster · ACM SIGAPL APL Quote Quad · 1981
This paper proposes two related extensions to APL: the extension of assignment to allow a name F to be assigned to a derived function by an expression of the form F ←+.x, and the introduction of a dyadic operator @@@@ to apply to character arrays D and M so that D @@@@ M produces an ambivalent function in which the dyadic case is defined by D and the monadic case by M .