Mirror of forum.nim-lang.org

5950 :: How to expand a single template

• DeletedUser (orginal) [2020-02-19T08:26:20+01:00] view original

  I have this snippet

  
  import macros
  
  template texture(a, b): untyped =
    var a: TexturePtr
    
    init:
      state.a = loadTexture(b)
    
    finish:
      state.a.free()
  
  static:
    let node = getAst(texture(background, "res/menu.png")) # undeclared identifier: background
    let node = getAst(quote do: texture(background, "res/menu.png")) # undeclared identifier: TexturePtr
  Run

  I want an option that doesn't error and returns this AST:

  
  var background: TexturePtr
  
  init:
    state.background = loadTexture("res/menu.png")
  
  finish:
    state.background.free()
  Run

  Basically gives the result of a single template expanded, not expanded all the way to the point of type checking. Does Nim have a hook for this?

---

• Araq (orginal) [2020-02-19T08:41:24+01:00] view original

  template + getAst seems to be a good idea, but you need to use getAst inside a macro.

---

• DeletedUser (orginal) [2020-02-19T08:59:27+01:00] view original

  I think I understand now, the template args in getAst have to be NimNodes. One more question, can you dynamically evaluate template expansions based on existing AST or is it conceptually unviable? Example:

  import macros
  
  template texture(a, b): untyped =
    var a: TexturePtr
    
    init:
      state.a = loadTexture(b)
    
    finish:
      state.a.free()
  
  macro mcr(body) =
    result = newEmptyNode()
    let node = getAst(`body[0]`) # do what here?
    echo body.treeRepr
  
  mcr:
    texture background, "res/menu.png"
  Run

---