[Nim] Balanced Pairs

proc balancedPairs(s: string, a: char): seq[string] =

  proc openPos(s: string, a: char): seq[int] =
    var seqOpenpos = newSeq[int]()
    for i in 0..s.len - 1:
      if s[i] == a: seqOpenpos.add(i)
    result = seqOpenpos 

  proc boundSearch(s: string, a, b: char, n: int): string =
    var
      iopen: int
      level = 0
    for i in n..s.len - 1:
      if s[i] == a:
        if level == 0: iopen = i
        level += 1
      elif s[i] == b:
        level -= 1
        if level == 0: 
          return s[iopen..i]
    result = ""  

  var 
    seqBalanced = newSeq[string]()
    aPairs = ['(', '{', '[', '<', ')', '}', ']', '>']
    b = ' '
    sop: seq[int]

  # get the counterpart char
  for i in 0..3:
    if aPairs[i] == a: b = aPairs[i + 4]
  
  if b != ' ':
    sop = s.openPos(a)
    for i in sop: seqBalanced.add(s.boundSearch(a, b, i))

  result = seqBalanced    
 
 
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let sNested = "(1st bound (nested #1 (nested #2)) 1st (neighbour nested #1) 1st)"
let bp = sNested.balancedPairs('(')
echo bp

# result: @["(1st bound (nested #1 (nested #2)) 1st (neighbour nested #1) 1st)", "(nested #1 (nested #2))", "(nested #2)", "(neighbour nested #1)"]
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