added helper functions for easier creation of AST nodes

stl/__init__.py

@@ -1,4 +1,5 @@
 from stl.utils import terms_lens, lineq_lens, walk, tree, and_or_lens
+from stl.utils import alw, env, andf, orf
 from stl.ast import dt_sym, t_sym
 from stl.ast import LinEq, Interval, NaryOpSTL, Or, And, F, G, ModalOp, Neg, Var, AtomicPred
 from stl.parser import parse

stl/utils.py

@@ -1,5 +1,7 @@
 from typing import List, Type, Dict, Mapping, T
 from collections import deque
+import operator as op
+from functools import reduce
 
 from lenses import lens, Lens
 import funcy as fn
@@ -127,3 +129,19 @@ def to_mtl(phi:STL) -> MTL:
 def from_mtl(phi:MTL, ap_map:Dict[AtomicPred, LinEq]) -> STL:
     focus = AP_lens(phi)
     return focus.modify(ap_map.get)
+
+
+def alw(phi, *, lo, hi):
+    return G(Interval(lo, hi), phi)
+
+def env(phi, *, lo, hi):
+    return F(Interval(lo, hi), phi)
+
+def until(phi, *, lo, hi):
+    raise NotImplementedError
+
+def andf(*args):
+    return reduce(op.and_, args)
+
+def orf():
+    return reduce(op.or_, args)