Type StringArray
    elements(Any) As String
    length As Integer
End Type

Type ItemResult
    items As StringArray
    remaining As String
End Type

Type GroupResult
    items As StringArray
    remaining As String
    success As Boolean
End Type

Declare Function GetGroup(s As String, depth As Integer) As GroupResult
Declare Function GetItem(s As String, depth As Integer = 0) As ItemResult

Function ConcatArrays(arr1 As StringArray, arr2 As StringArray) As StringArray
    Dim result As StringArray
    Dim totalLen As Integer = arr1.length * arr2.length
    Redim result.elements(totalLen - 1)
    result.length = totalLen

    Dim idx As Integer = 0
    For i As Integer = 0 To arr1.length - 1
        For j As Integer = 0 To arr2.length - 1
            result.elements(idx) = arr1.elements(i) & arr2.elements(j)
            idx += 1
        Next j
    Next i

    Return result
End Function

Function GetItem(s As String, depth As Integer = 0) As ItemResult
    Dim result As ItemResult
    Redim result.items.elements(0)
    result.items.elements(0) = ""
    result.items.length = 1

    While Len(s) > 0
        Dim c As String = Left(s, 1)

        If depth > 0 Andalso (c = "," Orelse c = "}") Then
            result.remaining = s
            Return result
        Elseif c = "{" Then
            Dim groupResult As GroupResult = GetGroup(Mid(s, 2), depth + 1)
            If groupResult.success Then
                result.items = ConcatArrays(result.items, groupResult.items)
                s = groupResult.remaining
                Continue While
            End If
        Elseif c = "\" Andalso Len(s) > 1 Then
            s = Mid(s, 2)
            c = "\" & Left(s, 1)
        End If

        For i As Integer = 0 To result.items.length - 1
            result.items.elements(i) &= c
        Next
        s = Mid(s, 2)
    Wend

    result.remaining = s
    Return result
End Function

Function GetGroup(s As String, depth As Integer) As GroupResult
    Dim result As GroupResult
    Dim comma As Boolean = False
    result.success = False
    Redim result.items.elements(0)
    result.items.length = 0

    While Len(s) > 0
        Dim itemResult As ItemResult = GetItem(s, depth)
        If Len(itemResult.remaining) = 0 Then Exit While

        s = itemResult.remaining

        If result.items.length = 0 Then
            result.items = itemResult.items
        Else
            Dim newLen As Integer = result.items.length + itemResult.items.length
            Redim Preserve result.items.elements(newLen - 1)
            For i As Integer = 0 To itemResult.items.length - 1
                result.items.elements(result.items.length + i) = itemResult.items.elements(i)
            Next
            result.items.length = newLen
        End If

        If Left(s, 1) = "}" Then
            result.success = True
            If comma Then
                result.remaining = Mid(s, 2)
                Return result
            End If

            For i As Integer = 0 To result.items.length - 1
                result.items.elements(i) = "{" & result.items.elements(i) & "}"
            Next
            result.remaining = Mid(s, 2)
            Return result
        End If

        If Left(s, 1) = "," Then
            comma = True
            s = Mid(s, 2)
        End If
    Wend

    Return result
End Function

' Main program
Dim testStrings(3) As String
testStrings(0) = "~/{Downloads,Pictures}/*.{jpg,gif,png}"
testStrings(1) = "It{{em,alic}iz,erat}e{d,}, please."
testStrings(2) = "{,{,gotta have{ ,\, again\, }}more }cowbell!"
testStrings(3) = "{}} some }{,{\\{ edge, edge} \,}{ cases, {here} \\\\\}"

For i As Integer = 0 To 3
    Print testStrings(i) & Chr(10) & String(44, "-")
    Dim result As ItemResult = GetItem(testStrings(i))
    For j As Integer = 0 To result.items.length - 1
        Print result.items.elements(j)
    Next
    Print
Next

Sleep