scala - Why shapeless `everywhere` combinator works inside a method but not in a `val`? -

given code:

import shapeless._ import poly._  object everywherevalanddef {    sealed trait tree[t]   case class leaf[t](t: t) extends tree[t]   case class node[t](left: tree[t], right: tree[t]) extends tree[t]    val tree: tree[int] =     node(       node(         node(           leaf(1),           node(             leaf(2),             leaf(3))),         leaf(4)),       node(         leaf(5),         leaf(6)))    object inc extends ->((i: int) => + 1)    def afterincdef = everywhere(inc)(tree) // works    val afterincval = everywhere(inc)(tree) // fails    val expected: tree[int] =     node(       node(         node(           leaf(2),           node(             leaf(3),             leaf(4))),         leaf(5)),       node(         leaf(6),         leaf(7)))    def eqdef = expected == afterincdef    def eqval = expected == afterincval  } 

in repl session results:

welcome scala version 2.11.4 (java hotspot(tm) 64-bit server vm, java 1.8.0_25). type in expressions have them evaluated. type :help more information.  scala> everywherevalanddef.eqdef res0: boolean = true  scala> everywherevalanddef.eqval res1: boolean = false  scala> everywherevalanddef.tree res2: everywherevalanddef.tree[int] = node(node(node(leaf(1),node(leaf(2),leaf(3))),leaf(4)),node(leaf(5),leaf(6)))  scala> everywherevalanddef.afterincdef res3: everywherevalanddef.tree[int] = node(node(node(leaf(2),node(leaf(3),leaf(4))),leaf(5)),node(leaf(6),leaf(7)))  scala> everywherevalanddef.afterincval res4: everywherevalanddef.tree[int] = node(node(node(leaf(1),node(leaf(2),leaf(3))),leaf(4)),node(leaf(5),leaf(6))) 

why everywhere not working in val case?

if move definitions of tree, leaf , node out of everywherevalanddef top level (or other object) problem goes away.

i don't have definitive answer, appear subtle initialization order issue colliding scala macros issue.