diff --git a/acre/core.py b/acre/core.py
index 661d52e..1a22152 100644
--- a/acre/core.py
+++ b/acre/core.py
@@ -10,7 +10,7 @@
 PLATFORM = platform.system().lower()
 
 logging.basicConfig()
-log = logging.getLogger()
+log = logging.getLogger(__name__)
 
 
 class CycleError(ValueError):
@@ -44,14 +44,17 @@ def compute(env,
     # Collect dependencies
     dependencies = []
     for key, value in env.items():
-        dependent_keys = re.findall("{(.+?)}", value)
-        for dependency in dependent_keys:
-            # Ignore direct references to itself because
-            # we don't format with itself anyway
-            if dependency == key:
-                continue
+        try:
+            dependent_keys = re.findall("{(.+?)}", value)
+            for dependency in dependent_keys:
+                # Ignore direct references to itself because
+                # we don't format with itself anyway
+                if dependency == key:
+                    continue
 
-            dependencies.append((key, dependency))
+                dependencies.append((key, dependency))
+        except Exception:
+            dependencies.append((key, value))
 
     result = lib.topological_sort(dependencies)
 
@@ -66,6 +69,8 @@ def compute(env,
     # Format dynamic values
     for key in reversed(result.sorted):
         if key in env:
+            if not isinstance(env[key], str):
+                continue
             data = env.copy()
             data.pop(key)    # format without itself
             env[key] = lib.partial_format(env[key], data=data)
@@ -73,6 +78,8 @@ def compute(env,
     # Format cyclic values
     for key in result.cyclic:
         if key in env:
+            if not isinstance(env[key], str):
+                continue
             data = env.copy()
             data.pop(key)   # format without itself
             env[key] = lib.partial_format(env[key], data=data)
@@ -81,8 +88,12 @@ def compute(env,
     if dynamic_keys:
         formatted = {}
         for key, value in env.items():
-            new_key = lib.partial_format(key, data=env)
+            if not isinstance(value, str):
+                new_key = key
+                formatted[key] = value
+                continue
 
+            new_key = lib.partial_format(key, data=env)
             if new_key in formatted:
                 if not allow_key_clash:
                     raise DynamicKeyClashError("Key clashes on: {0} "
@@ -96,6 +107,8 @@ def compute(env,
     if cleanup:
         separator = os.pathsep
         for key, value in env.items():
+            if not isinstance(value, str):
+                continue
             paths = value.split(separator)
 
             # Keep unique path entries: {A};{A};{B} -> {A};{B}
@@ -138,7 +151,7 @@ def parse(env, platform_name=None):
 
         # Allow to have lists as values in the tool data
         if isinstance(value, (list, tuple)):
-            value = ";".join(value)
+            value = os.pathsep.join(value)
 
         result[variable] = value
 
@@ -151,12 +164,14 @@ def append(env, env_b):
     # todo: this function name might also be confusing with "merge"
     env = env.copy()
     for variable, value in env_b.items():
-        for path in value.split(";"):
-            if not path:
-                continue
-
-            lib.append_path(env, variable, path)
-
+        try:
+            for path in value.split(os.pathsep):
+                if not path:
+                    continue
+                lib.append_path(env, variable, path)
+        except Exception:
+            if not isinstance(value, str):
+                env[variable] = value
     return env
 
 
@@ -190,7 +205,7 @@ def get_tools(tools, platform_name=None):
             '"TOOL_ENV" environment variable not found. '
             'Please create it and point it to a folder with your .json '
             'config files.'
-         )
+        )
 
     # Collect the tool files to load
     tool_paths = []
@@ -219,12 +234,13 @@ def get_tools(tools, platform_name=None):
             continue
 
         tool_env = parse(tool_env, platform_name=platform_name)
+
         environment = append(environment, tool_env)
 
     return environment
 
 
-def merge(env, current_env):
+def merge(env, current_env, missing=None):
     """Merge the tools environment with the 'current_env'.
 
     This finalizes the join with a current environment by formatting the
@@ -236,16 +252,20 @@ def merge(env, current_env):
         env (dict): The dynamic environment
         current_env (dict): The "current environment" to merge the dynamic
             environment into.
+        missing (str): Argument passed to 'partial_format' during merging.
+            `None` should keep missing keys unchanged.
 
     Returns:
         dict: The resulting environment after the merge.
 
     """
-
     result = current_env.copy()
     for key, value in env.items():
-        value = lib.partial_format(value, data=current_env, missing="")
-        result[key] = value
+        if not isinstance(value, str):
+            value = str(value)
 
-    return result
+        value = lib.partial_format(value, data=current_env, missing=missing)
 
+        result[key] = str(value)
+
+    return result
diff --git a/acre/lib.py b/acre/lib.py
index 09b3062..ca312da 100644
--- a/acre/lib.py
+++ b/acre/lib.py
@@ -1,4 +1,5 @@
 import os
+import re
 import string
 
 from collections import defaultdict, namedtuple
@@ -37,12 +38,24 @@ class FormatDict(dict):
         Missing keys are replaced with the return value of __missing__.
 
         """
+
         def __missing__(self, key):
             return missing.format(key=key)
 
     formatter = string.Formatter()
     mapping = FormatDict(**data)
-    return formatter.vformat(s, (), mapping)
+    try:
+        f = formatter.vformat(s, (), mapping)
+    except Exception:
+        r_token = re.compile(r"({.*?})")
+        matches = re.findall(r_token, s)
+        f = s
+        for m in matches:
+            try:
+                f = re.sub(m, m.format(**data), f)
+            except (KeyError, ValueError):
+                continue
+    return f
 
 
 def topological_sort(dependency_pairs):
@@ -68,10 +81,12 @@ def topological_sort(dependency_pairs):
     return Results(ordered, cyclic)
 
 
-def append_path(self, key, path):
-    """Append *path* to *key* in *self*."""
-    try:
-        if path not in self[key]:
-            self[key] = os.pathsep.join([self[key], str(path)])
-    except KeyError:
-        self[key] = str(path)
+def append_path(env, key, path):
+    """Append *path* to *key* in *env*."""
+
+    orig_value = env.get(key)
+    if not orig_value:
+        env[key] = str(path)
+
+    elif path not in orig_value.split(os.pathsep):
+        env[key] = os.pathsep.join([orig_value, str(path)])
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..8ef3f1a
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,27 @@
+[project]
+version = "1.0.0"
+name = "acre"
+description = "Lightweight cross-platform environment management Python package that makes it trivial to launch applications in their own configurable working environment."
+readme = "README.md"
+authors = [
+    { name = "Roy Nieterau", email ="roy_nieterau@hotmail.com" },
+]
+license = { file = "LICENSE" }
+requires-python = ">=2.7"
+keywords = ["environment", "pipeline"]
+
+classifiers = [
+  "Topic :: Software Development",
+  "Topic :: Utilities",
+  "Intended Audience :: Developers",
+  "Topic :: Software Development :: Libraries :: Python Modules"
+]
+
+[project.urls]
+homepage = "https://github.com/BigRoy/acre"
+repository = "https://github.com/BigRoy/acre"
+documentation = "https://github.com/BigRoy/acre"
+
+[build-system]
+requires = ["setuptools >= 35.0.2", "wheel"]
+build-backend = "setuptools.build_meta"
diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..6479c8b
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,20 @@
+[metadata]
+name = acre
+version = 1.0.0
+description = Lightweight cross-platform environment management Python package that makes it trivial to launch applications in their own configurable working environment
+long_description = file: README.md, LICENSE.md
+keywords = environment, pipeline
+license = GNU Lesser General Public License v3 (LGPLv3)
+classifiers =
+    Topic :: Software Development
+    License :: OSI Approved :: GNU Lesser General Public License v3 (LGPLv3)
+    Topic :: Utilities
+    Intended Audience :: Developers
+    Topic :: Software Development :: Libraries :: Python Modules
+
+[options]
+zip_safe = True
+include_package_data = True
+packages = find:
+install_requires =
+    importlib; python_version == "2.7"
diff --git a/setup.py b/setup.py
new file mode 100644
index 0000000..bac24a4
--- /dev/null
+++ b/setup.py
@@ -0,0 +1,6 @@
+#!/usr/bin/env python
+
+import setuptools
+
+if __name__ == "__main__":
+    setuptools.setup()
diff --git a/tests/test_dynamic_environments.py b/tests/test_dynamic_environments.py
index d039d11..4558ecb 100644
--- a/tests/test_dynamic_environments.py
+++ b/tests/test_dynamic_environments.py
@@ -131,6 +131,22 @@ def test_compute_preserve_reference_to_self(self):
             "PYTHONPATH": "x;y/{PYTHONPATH}"
         })
 
+    def test_compute_reference_formats(self):
+        """acre.compute() will correctly skip unresolved references."""
+        data = {
+            "A": "a",
+            "B": "{A},b",
+            "C": "{C}",
+            "D": "{D[x]}",
+        }
+        data = acre.compute(data)
+        self.assertEqual(data, {
+            "A": "a",
+            "B": "a,b",
+            "C": "{C}",
+            "D": "{D[x]}"
+        })
+
     def test_append(self):
         """Append paths of two environments into one."""