Dyalog Forums

Dear All,
i start to use recursive D-fns, and i try sample in immediate selfhelp (F1).

on recursive page, i understand fact function.

but for pow function, i dont understand. it illustrate ∇∇ and use only ∇.
what's the crumble ?

other points : i paste in APL session, and it do an error :

      pow←{             ⍝ Function power.
     ⍺=0:⍵         ⍝ Apply function operand ⍺ times.
     (⍺-1)∇ ⍺⍺ ⍵   ⍝ ⍺⍺ ⍺⍺ ⍺⍺ ... ⍵
 }
      2 pow 5
VALUE ERROR
pow[1] ⍺=0:⍵         ⍝ Apply function operand ⍺ times.
        ∧
      pow 5
SYNTAX ERROR
      pow 5
      ∧

i dont understand what can i do.
i am lost outer space. can you help me to contact Houston ?

Great Thanks,
Yves

Welcome to the world of operators :)
In this case you need a function as the left operand.
Perhaps this gives some ideas:

      ⍟⍟⍟⍟ 5000
¯0.2720968003
       4 ⍟ pow 5000
¯0.2720968003

-Veli-Matti

Dear -Veli-Matti,
Great thanks for your help.

      'bee' ⎕wc 'form' ( 'coord'  'pixel' )
      bee.AcceptFiles ← 1
      bee.onDropFiles ← 'AffMsg'
┌→───────────────────────────────────────────────────────────┐
│       ┌→────────┐ ┌→────────────────────────────────┐      │
│ #.bee │DropFiles│ │ ┌→────────────────────────────┐ │ ¯1 0 │
│       └─────────┘ │ │C:\Users\user\Desktop\yes.dws│ │      │
│                   │ └─────────────────────────────┘ │      │
│                   └∊────────────────────────────────┘      │
└∊───────────────────────────────────────────────────────────┘

how to catch path simply with never error ? (i do always mistake or error)

      disp 1↑ 2↓ chn
┌→────────────────────────────────────┐
│ ┌→────────────────────────────────┐ │
│ │ ┌→────────────────────────────┐ │ │
│ │ │C:\Users\user\Desktop\yes.dws│ │ │
│ │ └─────────────────────────────┘ │ │
│ └∊────────────────────────────────┘ │
└∊────────────────────────────────────┘

usualy, i handcraft a trashable and piggy code.
Now, with your help, i do this :

      disp { (≡⍵) (⊃,/) pow ⍵ } 1↑ 2↓ chn
┌→────────────────────────────┐
│C:\Users\user\Desktop\yes.dws│
└─────────────────────────────┘

possible my solution is not the better solution.
i appreciate yours comments on it.
Yves

Bonjour Yves ;-)

let me help to make it shorter:
with msg=


you can also do this:

Dear Michael & All,
Many Thanks for your help.

Before, i use only array with indexing.
Now, i see difference between them.

      ]display str ← 'abc'  'def'  'ghi'
┌→──────────────────┐
│ ┌→──┐ ┌→──┐ ┌→──┐ │
│ │abc│ │def│ │ghi│ │
│ └───┘ └───┘ └───┘ │
└∊──────────────────┘
      ]display 2 ⊃ str
┌→──┐
│def│
└───┘
      ]display str[ 2 ]
┌───────┐
│ ┌→──┐ │
│ │def│ │
│ └───┘ │
└∊──────┘

Thank you so much Michael
Guten Tag :-)