Mirror of forum.nim-lang.org

4441 :: How do you pass code blocks to when compiles?

• solo989 (orginal) [2018-12-07T13:00:51+01:00] view original

  This doesn't seem to work.

  when compiles(proc hello() = echo "hi"):
    proc hello() = echo "hi"
  Run

  but passing the code into a macro does.

  import macros
  macro tester(): untyped =
    let procDef = nnkProcDef.newTree(
      ident("hello"),
      newEmptyNode(),
      newEmptyNode(),
      nnkFormalParams.newTree(
        newEmptyNode()
      ),
      newEmptyNode(),
      newEmptyNode(),
      nnkStmtList.newTree(
        nnkCommand.newTree(
          newIdentNode("echo"),
          newLit("hi")
        )
      )
    )
    var whenStmt = nnkWhenStmt.newTree(
      nnkElifBranch.newTree(
        nnkCall.newTree(
          newIdentNode("compiles"),
          nnkStmtListExpr.newTree(procDef)
        )
      )
    )
    #treeRepr looks identical to the quote do version
    #but it will fail
    var whenStmt2 = nnkWhenStmt.newTree(
      nnkElifBranch.newTree(
        nnkCall.newTree(
          newIdentNode("compiles"),
          nnkStmtListExpr.newTree(procDef)
        ),
        newStmtList(procDef,nnkCommand.newTree(ident"echo",newLit("bye")))
      )
    )
    whenStmt[0].add quote do:
      proc hello() =
        echo "hi"
      echo "bye"
    #result = newStmtList(procDef)
    result = newStmtList(whenStmt)
    echo treeRepr result
    echo repr result
    echo treeRepr whenStmt2
  
  tester()
  hello()
  Run

  oddly enough if you use whenStmt2 instead of the quote do version proc hello won't exist so that's another problem altogether

---

• def (orginal) [2018-12-07T13:26:28+01:00] view original

  By making it anonymous and calling the proc you define:

  import macros
  when compiles((proc() =
    echo "hi"
    echo "foo"
    echo "bar")()):
    proc hello() = echo "hi"
  Run

---

• GULPF (orginal) [2018-12-07T14:17:52+01:00] view original

  The cleanest way is to wrap it in a block: ... expression:

  when compiles((block:
          echo "test 1"
          echo "test 2")):
      discard
  Run

---

• solo989 (orginal) [2018-12-07T14:38:21+01:00] view original

  My intention was to check to see if a proc hello exists in the current scope that doesn't conflict with the proc I'm about to create. If there is a better way to check to see if a proc already exists that conflicts I'm open to suggestions. The macro way of doing it seems to work as you pass a nnkStmtListExpr.newTree into it. I was just wondering if there was a nicer way to do it without generating a bunch of NimNodes.

---

• gemath (orginal) [2018-12-08T14:02:41+01:00] view original

  My intention was to check to see if a proc hello exists in the current scope that doesn't conflict with the proc I'm about to create.

  A simple test call to the proc would do (when compiles(hello()): ...). But then, the compiler would issue an error anyway if there's a conflict with an existing proc, so why bother checking that in custom compile-time code?

---