Why APL? Why not? Just learn the good thing about APL and throw away the bad thing.
  APL is evaluated from Right to Left if there is not brackets. Arithmetic operator has no precedence.

   4 × 2 + 3
20
4 × (2 + 3)

20

  Yep, it is NOT 11,

Find three consecutive repeating numbers in a vector
Input: a vector: v = [1 2 2 2 4] Output: true if there is three consecutive repeating numbers in the vector
  v ← 1 2 2 2 4
v
┌→────────┐
│1 2 2 2 4│
└~────────┘

There is three two 2 2 2 in the $v$
My First solution
  repeat3 ←{+/∧/2=/3(↑,/)⍵}

repeat3 1 2 2 2 4

1

repeat3 1 1 2 2 3 2

0

My second solution, two characters shorter without no bracket
  {+/^/2=/↑3,/⍵} 1 1 1 2

1

/
2f  86
From RIDE, the symbol is like Reduce or Fold or N-wise Reduce
Reduce
    +/ 1 2 3 4
10

N-wise Reduce, or Rolling or Sliding window
    2,/ 1 2 3 4
1 2  2 3  3 4

3,/ 1 2 3 4 5
1 2 3  2 3 4  3 4 5

3(,/)1 2 3 4
1 2 3  2 3 4



2191  8593
Mix
I have no idea what does it mean "Mix" here Mix - from the dictionary, combine or put together to form one substance or mass.
    ↑ (1 2 3) (3 4 5) (1)
1 2 3
3 4 5
1 0 0

We can combine N-wise Reduce and Mix to generate a matrix as following
       ↑3(,/)1 2 2 2 3
1 2 2
2 2 2
2 2 3

Check whether three numbers are the same
         2=/ 1 1 2
1 0
2=/ 1 1 1
1 1

Once we have the bit mask we can use OR to check and Reduce.
         ^/ 2=/ 1 1 2
0
^/ 2=/ 1 1 1
1

We just found some similar pattern with following code,
= and , both are Dyalic function, 2 or 3 here could be 2-wise or 3-wise Reduce
       2(=/) 1 1 2
1 0
3(,/) 1 2 3 4
1 2 3  2 3 4

Decimal to Binary in APL
Given a decimal and Convert it to binary. Ex. 8 → 1 0 0 0 9 → 1 0 0 1
   bin3 ← {⍵ = 0 : 0 ⋄ 1↓{⍵ = 0 : 0 ⋄ q ← ⌊⍵÷2 ⋄ r ← 2|⍵ ⋄ (∇ q), r} ⍵}
bin3¨ ⍳ 10
┌→──────────────────────────────────────────────────────────────────────────────┐
│ ┌→┐ ┌→──┐ ┌→──┐ ┌→────┐ ┌→────┐ ┌→────┐ ┌→────┐ ┌→──────┐ ┌→──────┐ ┌→──────┐ │
│ │1│ │1 0│ │1 1│ │1 0 0│ │1 0 1│ │1 1 0│ │1 1 1│ │1 0 0 0│ │1 0 0 1│ │1 0 1 0│ │
│ └~┘ └~──┘ └~──┘ └~────┘ └~────┘ └~────┘ └~────┘ └~──────┘ └~──────┘ └~──────┘ │
└∊──────────────────────────────────────────────────────────────────────────────┘


APL does not support large number Ex. The code will fail. APL gives wrong answer.
    bin3 1082246073363339
┌→──────────────────────────────────────────────────────────────────────────────────────────────────┐
│1 1 1 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 0 0 0 0 1 1 0 0 1 1 0 0 0 0 1 1 0 0 1 0 1 0 1 1 1 0 0 1 0 0 0 0│
└~──────────────────────────────────────────────────────────────────────────────────────────────────┘