diff --git a/markup.py b/markup.py
new file mode 100755
index 0000000..6fe22c2
--- /dev/null
+++ b/markup.py
@@ -0,0 +1,271 @@
+#!/usr/bin/env python3
+#
+# Copyright (c) 2022 Alek Ratzloff
+# 
+# This program is free software: you can redistribute it and/or modify  
+# it under the terms of the GNU General Public License as published by  
+# the Free Software Foundation, version 3.
+#
+# This program is distributed in the hope that it will be useful, but 
+# WITHOUT ANY WARRANTY; without even the implied warranty of 
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
+# General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License 
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+import functools
+import random
+import re
+import string
+from typing import Protocol
+
+
+NAME_CHARS = string.ascii_letters + string.digits
+DIGIT_SET = set(string.digits)
+ESCAPES = {
+    "n": "\n",
+    "r": "\r",
+    "b": "\b",
+    "t": "\t",
+    "\\": "\\",
+    "'": "'",
+    '"': '"',
+}
+
+
+class MarkupCallable(Protocol):
+    """
+    Callable for macros.
+    """
+
+    def __call__(self, ctx: "MarkupContext", *args: str) -> str:
+        ...
+
+
+class MarkupContext:
+    def __init__(self):
+        self.macros: dict[str, MarkupCallable] = {}
+
+    def register_macro(self, name: str, callback: MarkupCallable):
+        self.macros[name] = callback
+
+    def get_macro(self, name: str) -> MarkupCallable:
+        if name not in self.macros:
+            raise Exception(f"Could not find macro with name `{name}`")
+        return self.macros[name]
+
+
+class MarkupExpr:
+    def render(self, ctx: MarkupContext) -> str:
+        return ""
+
+
+class MarkupRaw(MarkupExpr):
+    def __init__(self, text: str):
+        self.text = text
+
+    def render(self, ctx: MarkupContext) -> str:
+        return self.text
+
+
+class MarkupMacro(MarkupExpr):
+    def __init__(self, macro: str, args: list[MarkupExpr]):
+        self.macro = macro
+        self.args = args
+
+    def render(self, ctx: MarkupContext) -> str:
+        macro = ctx.get_macro(self.macro)
+        args = [arg.render(ctx) for arg in self.args]
+        return macro(ctx, *args)
+
+
+class MarkupParser:
+    def __init__(self, text: str):
+        self.text = text
+        self.pos = 0
+        self.parts: list[MarkupExpr] = []
+
+    @property
+    def c(self) -> str:
+        return self.ahead(1)
+
+    def render(self, ctx: MarkupContext) -> str:
+        self.parse()
+        return "".join([exp.render(ctx) for exp in self.parts])
+
+    def parse(self):
+        while self.c:
+            if self.c in r"\$":
+                mac = self.parse_macro()
+                self.parts += [mac]
+            else:
+                raw = self.parse_raw()
+                self.parts += [raw]
+
+    def parse_macro(self) -> MarkupExpr:
+        self.match("${")
+        self.skip_whitespace()
+        macro = self.parse_ident()
+        args = []
+        self.skip_whitespace()
+        while self.c and self.c != "}":
+            arg = self.parse_expr()
+            args += [arg]
+            self.skip_whitespace()
+        self.match("}")
+        return MarkupMacro(macro, args)
+
+    def parse_expr(self) -> MarkupExpr:
+        if self.c in ["\"", "\'"]:
+            return MarkupRaw(self.parse_macro_string())
+        elif self.c in NAME_CHARS:
+            return MarkupRaw(self.parse_ident())
+        elif self.is_match("${"):
+            return self.parse_macro()
+        else:
+            raise Exception(
+                "lost the thread around {self.text[self.pos:self.pos + 5]}..."
+            )
+
+    def parse_macro_string(self) -> str:
+        start = self.c
+        if self.c in ['"', "'"]:
+            self.adv()
+        else:
+            raise Exception("expected single quote (\") or double quote (')")
+        text = ""
+        while self.c and self.c != start:
+            if self.c == "\\":
+                self.adv()
+                if self.c in "nrbt\\'\"":
+                    text += ESCAPES[self.c]
+                    self.adv()
+                else:
+                    raise Exception(f"unknown escape `\\{self.c}`")
+            else:
+                text += self.c
+                self.adv()
+        if not self.c:
+            raise Exception("unterminated string")
+        self.adv()
+        return text
+
+    def parse_ident(self) -> str:
+        start = self.pos
+        while self.c and self.c in NAME_CHARS:
+            self.adv()
+        return self.text[start : self.pos]
+
+    def skip_whitespace(self):
+        while self.c and self.c in string.whitespace:
+            self.adv()
+
+    def parse_raw(self) -> MarkupExpr:
+        text = ""
+        while self.c and self.c not in r"\$":
+            text += self.c
+            self.adv()
+        return MarkupRaw(text)
+
+    def ahead(self, count: int) -> str:
+        return self.text[self.pos : self.pos + count]
+
+    def adv(self, n: int = 1):
+        self.pos += n
+
+    def match(self, c: str):
+        if self.is_match(c):
+            self.adv(len(c))
+        else:
+            raise Exception(f"expected `{c}`")
+
+    def is_match(self, c: str) -> bool:
+        if c == self.ahead(len(c)):
+            return True
+        else:
+            return False
+
+
+################################################################################
+# Utility functions
+################################################################################
+
+
+def render(text: str, ctx: MarkupContext | None = None) -> str:
+    if not ctx:
+        ctx = default_context()
+    assert ctx
+    parser = MarkupParser(text)
+    return parser.render(ctx)
+
+
+################################################################################
+# Bulitin functions
+################################################################################
+
+
+def macro_random(
+    ctx: MarkupContext, first: str | None = None, second: str | None = None, *tail: str
+) -> str:
+    """
+    Choose a random number.
+
+    If no arguments, chooses a random float between 0.0 and 1.0, exclusive.
+
+    If one argument, chooses a random integer between 1 and the provided number, inclusive.
+
+    If two arguments, chooses a random integer between the provided numbers, inclusive.
+    """
+    if first and second:
+        lo = int(first)
+        hi = int(second)
+        return str(random.randint(lo, hi))
+    elif first:
+        hi = int(first)
+        return str(random.randint(1, hi))
+    else:
+        return str(random.random())
+
+
+def macro_choose(ctx: MarkupContext, *choices: str):
+    "Choose a random item."
+    return random.choice(choices)
+
+
+def macro_round(ctx: MarkupContext, n: str, digits: str | None = None) -> str:
+    "round() function, same as Python's."
+    if digits:
+        res = round(float(n), int(digits))
+    else:
+        res = round(float(n))
+    return str(res)
+
+
+@functools.cache
+def default_context():
+    c = MarkupContext()
+    c.register_macro("random", macro_random)
+    c.register_macro("choose", macro_choose)
+    c.register_macro("round", macro_round)
+
+    return c
+
+
+################################################################################
+# Main
+################################################################################
+if __name__ == '__main__':
+    import sys
+    filename = '<stdin>'
+    if len(sys.argv) == 1:
+        text = sys.stdin.read()
+    else:
+        filename = sys.argv[1]
+        with open(filename) as fp:
+            text = fp.read()
+    try:
+        result = render(text)
+        print(result, end='')
+    except Exception as ex:
+        print(f"{filename}: {ex}")