
use std::cmp::PartialEq;

//

pub fn append_vectors_once<'a, T : PartialEq + Copy, F : FnMut(T)>( dst : &'a mut Vec<T>, src : &'a Vec<Vec<T>>, on_evaluate : Option<F> ) -> &'a mut Vec<T>
{
  if on_evaluate.is_none()
  {
    for vec in src
    {
      for el in vec
      {
        if !dst.contains( el )
        {
          dst.push( *el );
        }
      }
    }
  }
  else
  {
    unimplemented!( "callbacks is not implemented" );
  }

  dst
}

//

pub fn left_index<T : PartialEq + Copy, F : FnMut(T, T) -> bool>( src : &Vec<T>, el : T, on_equalize : Option<F> ) -> Option<usize>
{
  if on_equalize.is_none()
  {
    return src.iter().position( | &x | x == el );
  }
  else
  {
    let mut equalizer = on_equalize.unwrap();
    for x in 0..src.len()
    {
      if equalizer( src[ x ], el )
      {
        return Some( x );
      }
    }
    return None
    // unimplemented!( "not implemented for callbacks" );
  }
}



use std::cmp::PartialEq;

//

pub fn append_vectors_once<'a, T : PartialEq + Copy, F : FnMut(T)>( dst : &'a mut Vec<T>, src : &'a Vec<Vec<T>>, on_evaluate : Option<F> ) -> &'a mut Vec<T>
{
  if on_evaluate.is_none()
  {
    for vec in src
    {
      for el in vec
      {
        if !dst.contains( el )
        {
          dst.push( *el );
        }
      }
    }
  }
  else
  {
    unimplemented!( "callbacks is not implemented" );
  }

  dst
}

//

pub fn left_index<T : PartialEq + Copy, F : FnMut(T)>( src : &Vec<T>, el : T, on_evaluate1 : Option<F> ) -> Option<usize>
{
  if on_evaluate1.is_none()
  {
    return src.iter().position( | &x | x == el );
  }
  else
  {
    unimplemented!( "not implemented for callbacks" );
  }
}


--- 
+++ 
@@ -28,15 +28,24 @@
 
 //
 
-pub fn left_index<T : PartialEq + Copy, F : FnMut(T)>( src : &Vec<T>, el : T, on_evaluate1 : Option<F> ) -> Option<usize>
+pub fn left_index<T : PartialEq + Copy, F : FnMut(T, T) -> bool>( src : &Vec<T>, el : T, on_equalize : Option<F> ) -> Option<usize>
 {
-  if on_evaluate1.is_none()
+  if on_equalize.is_none()
   {
     return src.iter().position( | &x | x == el );
   }
   else
   {
-    unimplemented!( "not implemented for callbacks" );
+    let mut equalizer = on_equalize.unwrap();
+    for x in 0..src.len()
+    {
+      if equalizer( src[ x ], el )
+      {
+        return Some( x );
+      }
+    }
+    return None
+    // unimplemented!( "not implemented for callbacks" );
   }
 }
 
Extend routine `left_index` by implementation for equalizer
