Mirror of forum.nim-lang.org

8229 :: Don't understand macros compile error

• xioren (orginal) [2021-07-13T07:43:40+02:00] view original

  I am trying to learn about macros and get the incredibly vague error

   Error: request to generate code for .compileTime proc: newProc
  Run

  when trying to compile:

  discard newProc(name=newIdentNode("test"),
                  params=[
                    newIdentNode("int"),
                    nnkIdentDefs.newTree(
                      newIdentNode("x"),
                      newIdentNode("int")
                      )
                    ],
                  body=nnkStmtList.newTree(
                        nnkInfix.newTree(
                          newIdentNode("+"),
                          newIdentNode("x"),
                          newLit(2)
                          )
                        )
                      )
  Run

  attempting to generate this proc:

  proc test(x: int): int =
    x + 2
  Run

  Any ideas?

---

• veksha (orginal) [2021-07-13T08:42:08+02:00] view original

  import macros
  macro gen() =
    newProc(name=newIdentNode("test"),
                  params=[
                    newIdentNode("int"),
                    nnkIdentDefs.newTree(
                      newIdentNode("x"),
                      newIdentNode("int"),
                      newNimNode(nnkEmpty)
                      )
                    ],
                  body=nnkStmtList.newTree(
                        nnkInfix.newTree(
                          newIdentNode("+"),
                          newIdentNode("x"),
                          newLit(2)
                          )
                        )
                      )
  gen
  Run

  echo test 44
  Run

---

• ynfle (orginal) [2021-07-13T08:51:03+02:00] view original

  newProc is procedure, not a macro. newProc takes NimNode s as input and returns NimNode s. Macros, however, output the NimNode as code not data, therefore as @veshka answered, if you call it in a macro then the NimNode AST returned from newProc will be expanded

---