diff --git a/stl/boolean_eval.py b/stl/boolean_eval.py
index 6693d56..0ea707b 100644
--- a/stl/boolean_eval.py
+++ b/stl/boolean_eval.py
@@ -7,7 +7,7 @@ from functools import singledispatch
 import funcy as fn
 import stl
 import stl.ast
-from lenses import lens
+from lenses import bind
 
 oo = float('inf')
 
@@ -129,7 +129,7 @@ def eval_stl_lineq(lineq):
 
 
 def eval_terms(lineq, x, t):
-    terms = lens(lineq).terms.each_().get_all()
+    terms = bind(lineq).terms.Each().collect()
     return sum(eval_term(term, x, t) for term in terms)
 
 
diff --git a/stl/utils.py b/stl/utils.py
index a9ea193..93e06a9 100644
--- a/stl/utils.py
+++ b/stl/utils.py
@@ -10,7 +10,7 @@ import lenses
 import stl.ast
 from lenses import lens
 from stl.ast import (AST, And, F, G, Interval, LinEq, NaryOpSTL,
-                     Neg, Or, Param)
+                     Neg, Or, Param, ModalOp)
 from stl.types import STL, STL_Generator
 
 Lens = TypeVar('Lens')
@@ -25,6 +25,19 @@ def walk(phi: STL) -> STL_Generator:
         yield node
         children.extend(node.children)
 
+def list_params(phi: STL):
+    """Walk of the AST."""
+    def get_params(leaf):
+        if isinstance(leaf, ModalOp):
+            if isinstance(leaf.interval[0], Param):
+                yield leaf.interval[0]
+            if isinstance(leaf.interval[1], Param):
+                yield leaf.interval[1]
+        elif isinstance(leaf, LinEq):
+            if isinstance(leaf.const, Param):
+                yield leaf.const
+    return set(fn.mapcat(get_params, walk(phi)))
+
 
 def vars_in_phi(phi):
     focus = stl.terms_lens(phi)
@@ -81,7 +94,7 @@ def terms_lens(phi: STL, bind: bool = True) -> Lens:
     return lineq_lens(phi, bind).Each().terms.Each()
 
 
-def param_lens(phi: STL) -> Lens:
+def param_lens(phi: STL, *, getter=False) -> Lens:
     def focus_lens(leaf):
         candidates = [lens.const] if isinstance(leaf, LinEq) else [
             lens.GetAttr('interval')[0],
@@ -89,7 +102,8 @@ def param_lens(phi: STL) -> Lens:
         ]
         return (x for x in candidates if isinstance(x.get()(leaf), Param))
 
-    return ast_lens(phi, pred=type_pred(LinEq, F, G), focus_lens=focus_lens)
+    return ast_lens(phi, pred=type_pred(LinEq, F, G), focus_lens=focus_lens, 
+                    getter=getter)
 
 
 def set_params(phi, val) -> STL: