[WIP] investigate tryExpr proposed by krux02

lib/std/tryexprs.nim

@@ -0,0 +1,55 @@
+# adapted from http://ix.io/2eL3
+
+import macros
+
+macro tryCompile*(expr, elseBody: untyped): untyped =
+  var name: NimNode
+
+  if expr.kind in nnkCallKinds:
+    if expr[0].kind == nnkDotExpr:
+      name = expr[0][1]
+    else:
+      name = expr[0]
+  else:
+    if expr.kind == nnkDotExpr:
+      name = expr[1]
+    else:
+      name = expr
+
+  expectKind(expr[0], nnkIdent)
+  let templateDef = nnkTemplateDef.newTree(
+    name,
+    newEmptyNode(),
+    newEmptyNode(),
+    nnkFormalParams.newTree(
+      newIdentNode("untyped"),
+      nnkIdentDefs.newTree(
+        newIdentNode("arg"),
+        newIdentNode("untyped"),
+        newEmptyNode()
+      )
+    ),
+    newEmptyNode(),
+    newEmptyNode(),
+    nnkStmtList.newTree(
+      elseBody
+    )
+  )
+
+  result = quote do:
+    `templateDef`
+    `expr`
+
+when isMainModule:
+  type
+    MyObject = object
+
+  var myInt: int = 123
+  var mySeq = @['a','b','c']
+  var myString = "abcdef"
+  var myObject: MyObject
+
+  doAssert tryCompile(myInt.len, 10) == 10
+  doAssert tryCompile(mySeq.len, 11) == 3
+  doAssert tryCompile(myString.len, 12) == 6
+  doAssert tryCompile(myObject.len, 13) == 13