diff --git a/bumpreqs/ir.py b/bumpreqs/ir.py
new file mode 100644
index 0000000..0426786
--- /dev/null
+++ b/bumpreqs/ir.py
@@ -0,0 +1,163 @@
+import re
+from dataclasses import dataclass, replace
+from typing import Generator, Optional
+
+from packaging.requirements import Requirement
+
+
+@dataclass
+class BaseNode:
+    def with_changes(self, **kwargs):
+        return replace(self, **kwargs)
+
+    def build(self, buf):
+        raise NotImplementedError
+
+    def dump(self, buf, indent=""):
+        raise NotImplementedError
+
+
+@dataclass
+class UnparsedLine(BaseNode):
+    orig_line: str
+
+    def build(self, buf):
+        buf.write(self.orig_line)
+
+    def dump(self, buf, indent=""):
+        buf.write(indent + repr(self) + "\n")
+
+
+@dataclass
+class VcsRequirementLine(BaseNode):
+    requirement: str
+    newline: str = "\n"
+
+    def build(self, buf):
+        buf.write(self.requirement)
+        buf.write(self.newline)
+
+    def dump(self, buf, indent=""):
+        buf.write(indent + repr(self) + "\n")
+
+
+@dataclass
+class LocalPathRequirementLine(BaseNode):
+    # ./foo
+    # -e ../foo
+    requirement: str
+    newline: str = "\n"
+
+    def build(self, buf):
+        buf.write(self.requirement)
+        buf.write(self.newline)
+
+    def dump(self, buf, indent=""):
+        buf.write(indent + repr(self) + "\n")
+
+
+@dataclass
+class RequirementLine(BaseNode):
+    # a parsed Requirement can't roundtrip
+    requirement: str
+    whitespace_before_requirement: str = ""
+    whitespace_after_requirement: str = ""
+    comment: str = ""
+    newline: str = "\n"
+
+    def build(self, buf):
+        buf.write(self.requirement)
+        buf.write(self.whitespace_before_requirement)
+        buf.write(self.whitespace_after_requirement)
+        buf.write(self.comment)
+        buf.write(self.newline)
+
+    def dump(self, buf, indent=""):
+        buf.write(indent + repr(self) + "\n")
+
+
+WELL_FORMED_REQUIREMENT_LINE = re.compile(
+    r"([ \t]*)([^# \t][^#]*?)([ \t]*)(#.*?)?(\r?\n)$"
+)
+
+
+@dataclass
+class RequirementFile:
+    children: [BaseNode] = ()
+
+    @classmethod
+    def parse(cls, data: str) -> "RequirementFile":
+        children: List[BaseNode] = []
+        if not data.endswith("\n"):
+            if "\r\n" in data:
+                data += "\r\n"
+            else:
+                data += "\n"
+
+        for line in data.splitlines(True):
+            match = WELL_FORMED_REQUIREMENT_LINE.match(line)
+            if not match:
+                children.append(UnparsedLine(line))
+                continue
+
+            (
+                whitespace_before_requirement,
+                value,
+                whitespace_after_requirement,
+                comment,
+                newline,
+            ) = match.groups()
+
+            if value.startswith(("-", "#")):
+                children.append(UnparsedLine(line))
+                continue
+            elif value.startswith((".", "/")):
+                assert whitespace_before_requirement == ""
+                assert whitespace_after_requirement == ""
+                assert not comment
+                children.append(LocalPathRequirementLine(value, newline))
+                continue
+            # N.b. see COMMENT_RE in pip/req/req_file.py
+            elif value and comment and not whitespace_after_requirement:
+                # TODO strip
+                value = value + whitespace_after_requirement + comment
+                children.append(VcsRequirementLine(value, newline))
+                continue
+            elif "://" in value:
+                assert whitespace_before_requirement == ""
+                assert whitespace_after_requirement == ""
+                assert not comment
+                children.append(VcsRequirementLine(value, newline))
+                continue
+
+            Requirement(value)  # validates
+
+            children.append(
+                RequirementLine(
+                    requirement=value,
+                    whitespace_before_requirement=whitespace_before_requirement,
+                    whitespace_after_requirement=whitespace_after_requirement,
+                    comment=comment,
+                    newline=newline,
+                )
+            )
+
+        return cls(children=children)
+
+    def build(self, buf):
+        for c in self.children:
+            c.build(buf)
+
+    def dump(self, buf, indent=""):
+        for c in self.children:
+            c.dump(buf, indent)
+
+
+if __name__ == "__main__":
+    import sys
+
+    try:
+        RequirementFile.parse(open(sys.argv[1]).read())
+    except Exception as e:
+        print(sys.argv[1])
+        raise