diff --git a/scripts/csv.py b/scripts/csv.py
index 21e34ad1..f6bc515e 100755
--- a/scripts/csv.py
+++ b/scripts/csv.py
@@ -654,7 +654,12 @@ class CsvExpr:
 
     # expr node base class
     class Expr:
-        def __init__(self, *args):
+        def __init__(self, *args, by=None):
+            self.by = by or []
+            for k in self.by:
+                if not isinstance(k, CsvExpr.Field):
+                    raise CsvExpr.Error("complicated by? %s" % k)
+
             for k, v in zip('abcdefghijklmnopqrstuvwxyz', args):
                 setattr(self, k, v)
 
@@ -668,8 +673,10 @@ class CsvExpr:
             return sum(1 for _ in self)
 
         def __repr__(self):
-            return '%s(%s)' % (
+            return '%s%s(%s)' % (
                     self.__class__.__name__,
+                    '[%s]' % (','.join(repr(k) for k in self.by))
+                        if self.by else '',
                     ','.join(repr(v) for v in self))
 
         def fields(self):
@@ -741,9 +748,14 @@ class CsvExpr:
 
     # func expr helper
     def func(funcs):
-        def func(name, args="a"):
+        def func(name, by=None, args=None):
+            if by is None and args is None:
+                by, args = None, "a"
+            elif args is None:
+                by, args = None, by
             def func(f):
                 f._func = name
+                f._fby = by
                 f._fargs = args
                 funcs[f._func] = f
                 return f
@@ -960,22 +972,16 @@ class CsvExpr:
                 return CsvGStddev()([v.eval(fields, state) for v in self])
 
     # enumerate exprs
-    @func('enumerate', '[*by]')
+    @func('enumerate', 'by', '')
     class Enumerate(Expr):
         """A [per by] number incremented for each result"""
         def fields(self):
-            # don't typecheck by fields
             return set()
 
         def type(self, types={}):
-            # don't typecheck, but make sure we can read by fields
-            for v in self:
-                if not isinstance(v, CsvExpr.Field):
-                    raise CsvExpr.Error("complicated by field? %s" % v)
             return CsvInt
 
         def fold(self, types={}):
-            # don't typecheck by fields
             return CsvSum
 
         def eval(self, fields={}, state=None):
@@ -984,7 +990,7 @@ class CsvExpr:
 
             # enumerate
             k = ('enumerate', id(self)) + tuple(
-                    fields.get(v.a) for v in self)
+                    fields.get(k.a) for k in self.by)
             x = state.get(k)
             if x is None:
                 z = 0
@@ -994,25 +1000,9 @@ class CsvExpr:
             state[k] = z
             return CsvInt(z)
 
-    @func('accumulate', 'a[, *by]')
+    @func('accumulate', 'by', 'a')
     class Accumulate(Expr):
         """A [per by] running sum across results"""
-        def fields(self):
-            # don't typecheck by fields
-            return self.a.fields()
-
-        def type(self, types={}):
-            # don't typecheck, but make sure we can read by fields
-            t = self.a.type(types)
-            for v in it.islice(self, 1, None):
-                if not isinstance(v, CsvExpr.Field):
-                    raise CsvExpr.Error("complicated by field? %s" % v)
-            return t
-
-        def fold(self, types={}):
-            # don't typecheck by fields
-            return self.a.fold(types)
-
         def eval(self, fields={}, state=None):
             y = self.a.eval(fields, state)
             if state is None:
@@ -1020,7 +1010,7 @@ class CsvExpr:
 
             # accumulate
             k = ('accumulate', id(self)) + tuple(
-                    fields.get(v.a) for v in it.islice(self, 1, None))
+                    fields.get(k.a) for k in self.by)
             x = state.get(k)
             if x is None:
                 z = y
@@ -1030,25 +1020,9 @@ class CsvExpr:
             state[k] = z
             return z
 
-    @func('delta', 'a[, *by]')
+    @func('delta', 'by', 'a')
     class Delta(Expr):
         """A [per by] difference between subsequent results"""
-        def fields(self):
-            # don't typecheck by fields
-            return self.a.fields()
-
-        def type(self, types={}):
-            # don't typecheck, but make sure we can read by fields
-            t = self.a.type(types)
-            for v in it.islice(self, 1, None):
-                if not isinstance(v, CsvExpr.Field):
-                    raise CsvExpr.Error("complicated by field? %s" % v)
-            return t
-
-        def fold(self, types={}):
-            # don't typecheck by fields
-            return self.a.fold(types)
-
         def eval(self, fields={}, state=None):
             y = self.a.eval(fields, state)
             if state is None:
@@ -1056,7 +1030,7 @@ class CsvExpr:
 
             # compute delta
             k = ('delta', id(self)) + tuple(
-                    fields.get(v.a) for v in it.islice(self, 1, None))
+                    fields.get(k.a) for k in self.by)
             x = state.get(k)
             if x is None:
                 z = y
@@ -1531,7 +1505,12 @@ class CsvExpr:
         print('funcs:')
         for func in cls.funcs.keys():
             print('  %-21s %s' % (
-                    '%s(%s)' % (func, CsvExpr.funcs[func]._fargs),
+                    '%s%s(%s)' % (
+                        func,
+                        '[%s]' % CsvExpr.funcs[func]._fby
+                            if CsvExpr.funcs[func]._fby
+                            else '',
+                        CsvExpr.funcs[func]._fargs),
                     CsvExpr.funcs[func].__doc__))
 
     # parse an expr
@@ -1560,6 +1539,25 @@ class CsvExpr:
             elif p.match('[_a-zA-Z][_a-zA-Z0-9]*'):
                 a = p.chomp()
 
+                by = None
+                if p.match('\['):
+                    p.chomp()
+                    if a not in CsvExpr.funcs:
+                        raise CsvExpr.Error("unknown function? %s" % a)
+                    by = []
+                    while True:
+                        if not p.match('\]'):
+                            b = p_expr(p)
+                            by.append(b)
+                            if p.match(','):
+                                p.chomp()
+                                continue
+                        if not p.match('\]'):
+                            raise CsvExpr.Error("mismatched squares? %s" % p)
+                        p.chomp()
+                        break
+
+                args = None
                 if p.match('\('):
                     p.chomp()
                     if a not in CsvExpr.funcs:
@@ -1575,8 +1573,12 @@ class CsvExpr:
                         if not p.match('\)'):
                             raise CsvExpr.Error("mismatched parens? %s" % p)
                         p.chomp()
-                        a = CsvExpr.funcs[a](*args)
                         break
+
+                if args is not None:
+                    a = CsvExpr.funcs[a](*args, by=by)
+                elif by is not None:
+                    raise CsvExpr.Error("expected parens? %s" % p)
                 else:
                     a = CsvExpr.Field(a)