Added oop_macro.nim.

oop_macro.nim

@@ -0,0 +1,233 @@
+import macros
+
+{.hint[XDeclaredButNotUsed]: off.}
+
+macro new*(obj: expr): expr {.immediate.}=
+    ## Replaces the new keyword to call an init
+    ## function if it exists
+    quote do:
+        var init_obj = `obj`
+        when compiles(init_obj.init()):
+            init_obj.init()
+        init_obj
+
+macro class*(head: expr, body: stmt): stmt {.immediate.} =
+  # The macro is immediate so that it doesn't
+  # resolve identifiers passed to it
+
+  # object reference name inside methods.
+  # ie: self, self
+  let obj_reference = "self"
+
+  var typeName, baseName: PNimrodNode
+
+  if head.kind == nnkIdent:
+    # `head` is expression `typeName`
+    # echo head.treeRepr
+    # --------------------
+    # Ident !"Animal"
+    typeName = head
+
+  elif head.kind == nnkInfix and $head[0] == "of":
+    # `head` is expression `typeName of baseClass`
+    # echo head.treeRepr
+    # --------------------
+    # Infix
+    #   Ident !"of"
+    #   Ident !"Animal"
+    #   Ident !"RootObj"
+    typeName = head[1]
+    baseName = head[2]
+
+  else:
+    quit "Invalid node: " & head.lispRepr
+
+  # echo treeRepr(body)
+  # --------------------
+  # StmtList
+  #   VarSection
+  #     IdentDefs
+  #       Ident !"name"
+  #       Ident !"string"
+  #       Empty
+  #     IdentDefs
+  #       Ident !"age"
+  #       Ident !"int"
+  #       Empty
+  #   MethodDef
+  #     Ident !"vocalize"
+  #     Empty
+  #     Empty
+  #     FormalParams
+  #       Ident !"string"
+  #     Empty
+  #     Empty
+  #     StmtList
+  #       StrLit ...
+  #   MethodDef
+  #     Ident !"age_human_yrs"
+  #     Empty
+  #     Empty
+  #     FormalParams
+  #       Ident !"int"
+  #     Empty
+  #     Empty
+  #     StmtList
+  #       DotExpr
+  #         Ident !"self"
+  #         Ident !"age"
+
+  # create a new stmtList for the result
+  result = newStmtList()
+
+  # var declarations will be turned into object fields
+  var recList = newNimNode(nnkRecList)
+
+  # add a super function to simulate OOP
+  # inheritance tree (Doesn't do what is expected because of dynamic binding)
+  #if not isNil(`baseName`):
+  #    var super = quote do:
+  #        proc super(self: `typeName`): `baseName`=
+  #          return `baseName`(self)
+  #   result.add(super)
+
+  # Make forward declarations so that function order
+  # does not matter, just like in real OOP!
+  for node in body.children:
+    case node.kind:
+      of nnkMethodDef, nnkProcDef:
+        # inject `self: T` into the arguments
+        let n = copyNimTree(node)
+        n.params.insert(1, newIdentDefs(ident(obj_reference), typeName))
+        # clear the body so we only get a
+        # declaration
+        n.body = newEmptyNode()
+        result.add(n)
+
+        # forward declare the inheritable method
+        let n2 = copyNimTree(n)
+        let proc_name = $(n2.name.toStrLit())
+        let type_name = $(typeName.toStrLit())
+        let new_name = ident(proc_name & type_name)
+        n2.name = new_name
+        result.add(n2)
+      else:
+          discard
+
+  # Iterate over the statements, adding `self: T`
+  # to the parameters of functions
+  for node in body.children:
+    case node.kind:
+      of nnkMethodDef, nnkProcDef:
+        # inject `self: T` into the arguments
+        let n = copyNimTree(node)
+        n.params.insert(1, newIdentDefs(ident(obj_reference), typeName))
+
+        # Copy the proc or method for inheritance
+        # ie: procName_ClassName()
+        let n2 = copyNimTree(node)
+        n2.params.insert(1, newIdentDefs(ident(obj_reference), typeName))
+        let proc_name = $(n2.name.toStrLit())
+        let type_name = $(typeName.toStrLit())
+        let new_name = ident(proc_name & type_name)
+        n2.name = new_name
+        result.add(n2)
+
+        # simply call the class method from here
+        # proc procName=
+        #    procName_ClassName()
+        var p: seq[PNimrodNode] = @[]
+        for i in 1..n.params.len-1:
+            p.add(n.params[i][0])
+        n.body = newStmtList(newCall(proc_name & type_name, p))
+
+        result.add(n)
+
+      of nnkVarSection:
+        # variables get turned into fields of the type.
+        for n in node.children:
+          recList.add(n)
+      else:
+        result.add(node)
+
+  # The following prints out the AST structure:
+  #
+  # import macros
+  # dumptree:
+  #   type X = ref object of Y
+  #     z: int
+  # --------------------
+  # TypeSection
+  #   TypeDef
+  #     Ident !"X"
+  #     Empty
+  #     RefTy
+  #       ObjectTy
+  #         Empty
+  #         OfInherit
+  #           Ident !"Y"
+  #         RecList
+  #           IdentDefs
+  #             Ident !"z"
+  #             Ident !"int"
+  #             Empty
+
+  var type_decl: PNimrodNode
+  if baseName == nil:
+    type_decl = quote do:
+      type `typeName` = ref object of RootObj
+  else:
+    type_decl = quote do:
+      type `typeName` = ref object of `baseName`
+
+  # Inspect the tree structure:
+  #
+  # echo type_decl.treeRepr
+  # --------------------
+  #   StmtList
+  #     TypeSection
+  #       TypeDef
+  #         Ident !"Animal"
+  #         Empty
+  #         RefTy
+  #           ObjectTy
+  #             Empty
+  #             OfInherit
+  #               Ident !"RootObj"
+  #             Empty   <= We want to replace self
+  type_decl[0][0][2][0][2] = recList
+  result.insert(0, type_decl)
+
+
+class Animal of RootObj:
+  var name: string
+  var age: int
+  method stuff(s:string): string = s
+  method vocalize: string = "..."
+  method age_human_yrs: int = self.age # `self` is injected
+
+class Dog of Animal:
+  method vocalize: string = "woof"
+  method age_human_yrs: int = self.age * 7
+
+class Cat of Animal:
+  method vocalize: string =
+      # call the base class method
+      self.vocalize_animal() & "meow"
+
+class Tiger of Cat:
+  method init()=
+      echo "I am a new tiger"
+  method vocalize: string =
+      # no need for super.super!
+      self.vocalize_animal() & "Rawr!"
+
+if isMainModule:
+    var animals: seq[Animal] = @[]
+    animals.add(new(Dog(name: "Sparky", age: 10)))
+    animals.add(new(Cat(name: "Mitten", age: 10)))
+    animals.add(new(Tiger(name: "Jean", age: 2)))
+
+    for a in animals:
+      echo a.name, " says ", a.vocalize()
+      echo a.age_human_yrs()