From e299490fb66afd0630dc9e30b9ee9c88dea88cc7 Mon Sep 17 00:00:00 2001
From: John Gerrard Holland <john_holland1@brown.edu>
Date: Thu, 6 Jul 2023 20:28:20 -0400
Subject: [PATCH] feat: add "append" to delta

---
 src/autora/workflow/state/delta.py | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/autora/workflow/state/delta.py b/src/autora/workflow/state/delta.py
index 27c46029..005f990c 100644
--- a/src/autora/workflow/state/delta.py
+++ b/src/autora/workflow/state/delta.py
@@ -6,12 +6,13 @@
 from collections import UserDict
 from dataclasses import dataclass, fields, replace
 from functools import singledispatch, wraps
-from typing import Generic, TypeVar
+from typing import Generic, List, TypeVar
 
 import numpy as np
 import pandas as pd
 
 S = TypeVar("S")
+T = TypeVar("T")
 
 
 @dataclass(frozen=True)
@@ -60,6 +61,19 @@ class State:
         >>> l.update(l=list("ghi"), m=list("rst"))
         ListState(l=['a', 'b', 'c', 'g', 'h', 'i'], m=['r', 's', 't'])
 
+        We can also define fields which `append` the last result:
+        >>> @dataclass(frozen=True)
+        ... class AppendState(State):
+        ...    n: List = field(default_factory=list, metadata={"delta": "append"})
+
+        >>> m = AppendState(n=list("ɑβɣ"))
+        >>> m
+        AppendState(n=['ɑ', 'β', 'ɣ'])
+
+        `n` will be appended:
+        >>> m + Delta(n="∂")
+        AppendState(n=['ɑ', 'β', 'ɣ', '∂'])
+
     """
 
     def __add__(self, other: Delta):
@@ -74,6 +88,9 @@ def __add__(self, other: Delta):
             if delta_behavior == "extend":
                 extended_value = extend(self_value, other_value)
                 updates[key] = extended_value
+            elif delta_behavior == "append":
+                appended_value = append(self_value, other_value)
+                updates[key] = appended_value
             elif delta_behavior == "replace":
                 updates[key] = other_value
             else:
@@ -154,6 +171,11 @@ def extend_pd_dataframe(a, b):
     return pd.concat((a, b), ignore_index=True)
 
 
+def append(a: List[T], b: T) -> List[T]:
+    # TODO: add DOCTESTS
+    return a + [b]
+
+
 @extend.register(np.ndarray)
 def extend_np_ndarray(a, b):
     """