Jot Operator

[KamakaniKing]

I see the following in the tutorials: f←(32∘+)∘(×∘1.8) for Fahrenheit to Celsius conversion. It seems that f←(32∘+)(×∘1.8) [i.e., no Jot in the center] fits the documentation description for Jot. Any reason for the center Jot?

[petermsiegel]

Not AFAIK. You can even leave out the parens:

      f←32∘+×∘1.8

[Adam|Dyalog]

Not sure which tutorial is being referred to. It may well be that it predates version 14.0 when trains were added to the language, and (32∘+)(×∘1.8) thus became valid.

Another reason could be that the example wants to show all three uses of ∘ as a dyadic operator.

You can even leave out the lefmost Jot:

      f←32+×∘1.8

[petermsiegel]

Of course, this is the most fun:

      f←(1.8÷⍨¯32∘+)⍣¯1  ⍝ inverse of c←1.8÷⍨¯32∘+
      f 20 30
      68 86

[KamakaniKing]

Thx Peter & Adam. The tutorial I was referring to was Mastering Dyalog APL by Bernard Legrand from 2009 - I know this is quite dated. That same function f←(32∘+)∘(×∘1.8) also shows up in the Dyalog Help version 18.0 as an example in several places, I think, such as for the Power Operator.

Adam - What is the 'third' use of dyadic jot exactly? I understand Bind {R}←A∘fY &
{R}←(f∘B)Y uses.

[Adam|Dyalog]

The third use is Beside (formerly Compose): f∘g where both f and g are functions. Documentation.