defining match syntax using Nim macro

matchmacro.nim

import macros

macro match(head, body: untyped): untyped =
  result = newNimNode nnkStmtList
  var casenode = newNimNode nnkCaseStmt
  casenode.add head
  
  for node in body:
    node.expectKind nnkInfix

    var ofbranch: NimNode
    case $node[0]
    of "->": ofbranch = newNimNode nnkOfBranch
    of "=>": ofbranch = newNimNode nnkElifBranch

    #var ofbranch = newNimNode nnkOfBranch
    for i in 1 ..< node.len:
      if i != node.len - 1 or node.kind != nnkStmtList:
        ofbranch.add node[i]
      else:
        ofbranch.add(newStmtList node[i])
    casenode.add ofbranch
  result.add casenode

expandMacros:
  match "3":
    "3" -> echo "it's 3"
    "4" -> echo "it's 4"

match "3":
  "3" -> echo "it's 3"
  "4" -> echo "4"

match 3 in @[1, 2, 3]:
  true -> echo "it's there"
  false -> echo "it's not there"

match "3":
  "nice" -> echo "3 is not nice"
  3 in @[1, 2, 3] => echo "haha, it works"