This is a feature request to allow cyclic imports. This allows to define mutually dependent types and procs (templates/macros) in different modules or in the same module regardless their definition order. Example:

# bar.nim
import foo
type Bar* = ref object
    f*: Foo
proc doSmthWithBar*(b: Bar) = discard
when isMainModule:
    let f = Foo.new()
    let b = Bar.new()
    f.doSmthWithFoo()
    f.b.doSmthWithBar()
    b.doSmthWithBar()
    b.f.doSmthWithFoo()

# foo.nim
import bar
type Foo* = ref object
    b*: Bar
proc doSmthWithFoo*(f: Foo) = discard
when isMainModule:
    let f = Foo.new()
    let b = Bar.new()
    f.doSmthWithFoo()
    f.b.doSmthWithBar()
    b.doSmthWithBar()
    b.f.doSmthWithFoo()

The symbol may be subjected to a cyclic lookup only if the following conditions are met:

• The symbol is a top level symbol.
• The symbol is defined by hand and is not a result of macro/template evaluation.
• The type of the symbol is not dependent on another template/macro global evaluation.

Forum discussion: https://forum.nim-lang.org/t/2114