[wdb] -- looking for list comparison similar to ''equal?'' in [Scheme],
I found that it is surprisingly difficult due to the lack of types.
Here my approach in Tcl. 
The procedure ''lequal'' checks recursively on elementwise equality:

===

proc lequal {a b} {
  if {![[string is list $a]] ||
      ![[string is list $b]]} then {
    string equal $a $b
  } elseif {[[llength $a]] != [[llength $b]]} then {
    return 0
  } elseif {[[llength $a]] == 0} then {
    return 1
  } elseif {[[llength $a]] > 1} then {        
    expr {[[lequal [[lindex $a 0]] [[lindex $b 0]]]] &&
          [[lequal [[lrange $a 1 end]] [[lrange $b 1 end]]]]}
  } elseif {$a eq [[lindex $a 0]] || $b eq [[lindex $b 0]]} then {
    string equal $a $b
  } else {
    lequal [[lindex $a 0]] [[lindex $b 0]]
  }
}

===

Don't know if in real life necessary, but by reasons of completeness, I did it.