diff --git a/setup.py b/setup.py
index 36fa0f3..9b54892 100644
--- a/setup.py
+++ b/setup.py
@@ -24,9 +24,13 @@ setup(
     packages=[
         "flowmetal",
     ],
-    scripts=[
-    ],
+    entry_points = {
+        'console_scripts': [
+            'iflow=flowmetal.repl:main'
+        ],
+    },
     install_requires=[
+        'prompt-toolkit~=3.0.0',
     ],
     extras_require={
     }
diff --git a/src/python/flowmetal/parser.py b/src/python/flowmetal/parser.py
index 0492676..fcd27a3 100644
--- a/src/python/flowmetal/parser.py
+++ b/src/python/flowmetal/parser.py
@@ -216,16 +216,21 @@ class Parser(SexpParser):
 
     @classmethod
     def parse(cls, f: PosTrackingBufferedReader):
-        if f.peek() == "(":
-            return cls.parse_list(f)
-        elif f.peek() == "[":
-            return cls.parse_sqlist(f)
-        elif f.peek() == '"':
-            return cls.parse_str(f)
+        if not f.peek():
+            raise SyntaxError(f"Got end of file ({f.pos()}) while parsing")
+        elif cls.ispunct(f.peek()):
+            if f.peek() == "(":
+                return cls.parse_list(f)
+            elif f.peek() == "[":
+                return cls.parse_sqlist(f)
+            elif f.peek() == '"':
+                return cls.parse_str(f)
+            elif f.peek() == ";":
+                return cls.parse_comment(f)
+            else:
+                raise SyntaxError(f"Got unexpected punctuation {f.read()!r} at {f.pos()} while parsing")
         elif cls.isspace(f.peek()):
             return cls.parse_whitespace(f)
-        elif f.peek() == ";":
-            return cls.parse_comment(f)
         else:
             return cls.parse_symbol(f)
 
@@ -258,6 +263,8 @@ class Parser(SexpParser):
             pos = rtb.pos()
             acc = []
             while f.peek() != closec:
+                if not f.peek():
+                    raise SyntaxError(f"Got end of file ({f.pos()}) while parsing {openc!r}...{closec!r} starting at {pos}")
                 acc.append(cls.parse(rtb))
             assert rtb.read() == closec  # Discard the trailing delimeter
             return ctor(acc, str(rtb), pos)
diff --git a/src/python/flowmetal/repl.py b/src/python/flowmetal/repl.py
new file mode 100644
index 0000000..a834877
--- /dev/null
+++ b/src/python/flowmetal/repl.py
@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+
+import argparse
+import logging
+import sys
+import pprint
+
+from flowmetal.syntax_analyzer import analyzes
+
+from prompt_toolkit import print_formatted_text, prompt, PromptSession
+from prompt_toolkit.formatted_text import FormattedText
+from prompt_toolkit.history import FileHistory
+from prompt_toolkit.styles import Style
+
+
+STYLE = Style.from_dict({
+    # User input (default text).
+    "": "",
+    "prompt": "ansigreen",
+    "time": "ansiyellow"
+})
+
+
+class InterpreterInterrupt(Exception):
+  """An exception used to break the prompt or evaluation."""
+
+
+parser = argparse.ArgumentParser()
+
+def main():
+    """REPL entry point."""
+
+    args = parser.parse_args(sys.argv[1:])
+    logger = logging.getLogger("arrdem.datalog")
+    ch = logging.StreamHandler()
+    ch.setLevel(logging.INFO)
+    formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
+    ch.setFormatter(formatter)
+    logger.addHandler(ch)
+
+    session = PromptSession(history=FileHistory(".datalog.history"))
+    line_no = 0
+
+    while True:
+        try:
+            line = session.prompt([("class:prompt", ">>> ")], style=STYLE)
+        except (InterpreterInterrupt, KeyboardInterrupt):
+            continue
+        except EOFError:
+            break
+
+        try:
+            pprint.pprint(analyzes(line, source_name=f"repl@{line_no}"))
+        except Exception as e:
+            print(e)
+        finally:
+            line_no += 1