urbit/pub/doc/hoon/runes/br/brtr.md

bartar, |*, %brtr

Wet gate

|* is a synthetic hoon that produces a wet gate with sample $*(p), arm q. A gate is a core with one arm, $, the empty name.

|* is similar to a function in the same way that |= is, but differs in that it does type checking at runtime. With |*, the product type is checked to be the same as the input type, rather than the sample tile.

See also

bartis, |=, %brts

Produces

Twig: [%brtr p=tile q=twig]

Sample

p is a tile. q is a twig.

Tall form

|*  p
    q

Wide form

|*(p q)

Irregular form

None

Examples

~zod/try=> %.('c' |*(a=@ a))
'c'
~zod/try=> %.('c' |=(a=@ a))
99

This is a concise way of understanding the difference between |* and |=. We use %. in both cases to slam each gate with the sample 'c'. |= uses its tile a=@ to cast 'c' to an atom (99 is the ASCII code for 'c'). |* simply ensures that the product type matches the input sample type.

++  flop                                                ::  reverse
      ~/  %flop
      |*  a=(list)
      =>  .(a (homo a))
      ^+  a
      =+  b=`_a`~
      |-
      ?@  a
        b
      $(a t.a, b [i.a b])

In ++flop, |* is used so the type information within the passed in list is maintained. Without a |*, any cords would be cast to nouns as in our previous example.