From c405400496dce580a0eb0c4abdcd3ffbb5cabb8f Mon Sep 17 00:00:00 2001
From: Vadim Laletin <rusmiligamer@gmail.com>
Date: Wed, 29 Apr 2026 08:54:11 +0000
Subject: [PATCH] #68: Support for coalesce function

Co-Authored-By: Claude <noreply@anthropic.com>
---
 fhirpathpy/engine/__init__.py               |  8 +++++
 fhirpathpy/engine/invocations/__init__.py   |  1 +
 fhirpathpy/engine/invocations/combining.py  |  9 ++++++
 fhirpathpy/engine/invocations/navigation.py |  2 +-
 fhirpathpy/engine/nodes.py                  |  4 +++
 pyproject.toml                              |  1 +
 tests/cases/5.2.8_coalesce.yaml             | 33 +++++++++++++++++++++
 7 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 tests/cases/5.2.8_coalesce.yaml

diff --git a/fhirpathpy/engine/__init__.py b/fhirpathpy/engine/__init__.py
index b50ba58..ce7c424 100644
--- a/fhirpathpy/engine/__init__.py
+++ b/fhirpathpy/engine/__init__.py
@@ -64,6 +64,14 @@ def doInvoke(ctx, fn_name, data, raw_params):
     if "nullable_input" in invocation and util.is_nullable(data):
         return []
 
+    if "variadic" in invocation:
+        tp = invocation["variadic"]
+        raw_params_list = raw_params if isinstance(raw_params, list) else []
+        thisValue = ctx["$this"] if "$this" in ctx else ctx["dataRoot"]
+        params = [make_param(ctx, thisValue, tp, pr) for pr in raw_params_list]
+        res = invocation["fn"](ctx, util.arraify(data), *params)
+        return util.arraify(res)
+
     if "arity" not in invocation:
         if raw_params is None or util.is_empty(raw_params):
             res = invocation["fn"](ctx, util.arraify(data))
diff --git a/fhirpathpy/engine/invocations/__init__.py b/fhirpathpy/engine/invocations/__init__.py
index c0966f7..2111b02 100644
--- a/fhirpathpy/engine/invocations/__init__.py
+++ b/fhirpathpy/engine/invocations/__init__.py
@@ -50,6 +50,7 @@
     "skip": {"fn": filtering.skip_fn, "arity": {1: ["Integer"]}},
     "intersect": {"fn": subsetting.intersect_fn, "arity": {1: ["AnyAtRoot"]}},
     "combine": {"fn": combining.combine_fn, "arity": {1: ["AnyAtRoot"]}},
+    "coalesce": {"fn": combining.coalesce_fn, "variadic": "Expr"},
     "iif": {"fn": misc.iif_macro, "arity": {2: ["Expr", "Expr"], 3: ["Expr", "Expr", "Expr"]}},
     "trace": {"fn": misc.trace_fn, "arity": {0: [], 1: ["String"]}},
     "toInteger": {"fn": misc.to_integer},
diff --git a/fhirpathpy/engine/invocations/combining.py b/fhirpathpy/engine/invocations/combining.py
index 364147f..5f2df62 100644
--- a/fhirpathpy/engine/invocations/combining.py
+++ b/fhirpathpy/engine/invocations/combining.py
@@ -1,3 +1,4 @@
+from fhirpathpy.engine import util
 from fhirpathpy.engine.invocations import existence
 
 """
@@ -15,3 +16,11 @@ def combine_fn(ctx, coll1, coll2):
 
 def exclude_fn(ctx, coll1, coll2):
     return [element for element in coll1 if element not in coll2]
+
+
+def coalesce_fn(ctx, data, *exprs):
+    for expr in exprs:
+        result = expr(data)
+        if not util.is_empty(result):
+            return result
+    return []
diff --git a/fhirpathpy/engine/invocations/navigation.py b/fhirpathpy/engine/invocations/navigation.py
index e6bbf95..f539f3d 100644
--- a/fhirpathpy/engine/invocations/navigation.py
+++ b/fhirpathpy/engine/invocations/navigation.py
@@ -58,7 +58,7 @@ def func(acc, res):
                     actualTypes = model["choiceTypePaths"].get(altPropName, [])
                     if len(actualTypes) > 0:
                         # If it is, we can use it
-                        fullPath = f"{res.propName}.{prop[:-len(childPath)]}"
+                        fullPath = f"{res.propName}.{prop[: -len(childPath)]}"
 
                 if isinstance(value, list):
                     mapped = [
diff --git a/fhirpathpy/engine/nodes.py b/fhirpathpy/engine/nodes.py
index f2b6de8..05c06c2 100644
--- a/fhirpathpy/engine/nodes.py
+++ b/fhirpathpy/engine/nodes.py
@@ -646,6 +646,8 @@ def __str__(self):
             return time_str
         return self.asStr
 
+    __hash__ = None
+
     def __eq__(self, other):
         if isinstance(other, str):
             return self.getTimeMatchStr()
@@ -734,6 +736,8 @@ def __str__(self):
             return iso_str
         return self.asStr
 
+    __hash__ = None
+
     def __eq__(self, other):
         if isinstance(other, str):
             return self.getDateTimeMatchStr()
diff --git a/pyproject.toml b/pyproject.toml
index 715b147..be26f8b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -2,6 +2,7 @@
 minversion = "6.0"
 addopts = "-ra -q --color=yes --cov=fhirpathpy --cov-report=xml"
 testpaths = ["tests"]
+filterwarnings = ["ignore::pytest.PytestRemovedIn9Warning"]
 log_cli = true
 log_cli_level = "INFO"
 python_functions = "*_test"
diff --git a/tests/cases/5.2.8_coalesce.yaml b/tests/cases/5.2.8_coalesce.yaml
new file mode 100644
index 0000000..e7c9b1a
--- /dev/null
+++ b/tests/cases/5.2.8_coalesce.yaml
@@ -0,0 +1,33 @@
+tests:
+  - desc: '5.2.8 coalesce'
+
+  - desc: '** returns first non-empty value from identifier'
+    expression: "coalesce(Patient.identifier.where(system='required-system').value.first(), 'unknown')"
+    result:
+      - required-value
+
+  - desc: '** returns fallback when first is empty'
+    expression: "coalesce(Patient.identifier.where(system='other-system').value.first(), 'unknown')"
+    result:
+      - unknown
+
+  - desc: '** returns first non-empty collection among multiple args'
+    expression: "coalesce({}, (1 | 2), (3 | 4))"
+    result:
+      - 1
+      - 2
+
+  - desc: '** returns single value when first arg is empty'
+    expression: "coalesce({}, 1)"
+    result:
+      - 1
+
+  - desc: '** returns empty when only arg is empty'
+    expression: "coalesce({})"
+    result: []
+
+subject:
+  resourceType: Patient
+  identifier:
+    - system: required-system
+      value: required-value