diff --git a/cranelift/isle/src/codegen.rs b/cranelift/isle/src/codegen.rs
index 4ffceb38c5..e080f30a25 100644
--- a/cranelift/isle/src/codegen.rs
+++ b/cranelift/isle/src/codegen.rs
@@ -470,20 +470,48 @@ impl<'a> TermFunctionsBuilder<'a> {
             }
         }
     }
+
+    fn finalize(self) -> (HashMap<TermId, TrieNode>, HashMap<TermId, TrieNode>) {
+        let functions_by_input = self
+            .builders_by_input
+            .into_iter()
+            .map(|(term, builder)| (term, builder.trie))
+            .collect::<HashMap<_, _>>();
+        let functions_by_output = self
+            .builders_by_output
+            .into_iter()
+            .map(|(term, builder)| (term, builder.trie))
+            .collect::<HashMap<_, _>>();
+        (functions_by_input, functions_by_output)
+    }
 }
 
-#[derive(Clone, Debug, Default)]
-pub struct Automata {
-    pub automata_by_input: HashMap<TermId, ()>,
-    pub automata_by_output: HashMap<TermId, ()>,
+#[derive(Clone, Debug)]
+pub struct Codegen<'a> {
+    typeenv: &'a TypeEnv,
+    termenv: &'a TermEnv,
+    functions_by_input: HashMap<TermId, TrieNode>,
+    functions_by_output: HashMap<TermId, TrieNode>,
 }
 
-impl Automata {
-    pub fn compile(typeenv: &TypeEnv, termenv: &TermEnv) -> Result<Automata, Error> {
+impl<'a> Codegen<'a> {
+    pub fn compile(typeenv: &'a TypeEnv, termenv: &'a TermEnv) -> Result<Codegen<'a>, Error> {
         let mut builder = TermFunctionsBuilder::new(typeenv, termenv);
         builder.build();
         log::trace!("builder: {:?}", builder);
-        // TODO
-        Ok(Automata::default())
+        let (functions_by_input, functions_by_output) = builder.finalize();
+        Ok(Codegen {
+            typeenv,
+            termenv,
+            functions_by_input,
+            functions_by_output,
+        })
+    }
+
+    pub fn generate_rust(&self) -> Result<String, Error> {
+        use std::fmt::Write;
+        let mut code = String::new();
+        writeln!(&mut code, "// GENERATED BY ISLE. DO NOT EDIT!")?;
+        Ok(code)
     }
 }
diff --git a/cranelift/isle/src/compile.rs b/cranelift/isle/src/compile.rs
index 3aa01e599c..618998980c 100644
--- a/cranelift/isle/src/compile.rs
+++ b/cranelift/isle/src/compile.rs
@@ -3,9 +3,9 @@
 use crate::error::Error;
 use crate::{ast, codegen, sema};
 
-pub fn compile(defs: &ast::Defs) -> Result<codegen::Automata, Error> {
+pub fn compile(defs: &ast::Defs) -> Result<String, Error> {
     let mut typeenv = sema::TypeEnv::from_ast(defs)?;
     let termenv = sema::TermEnv::from_ast(&mut typeenv, defs)?;
-    let automata = codegen::Automata::compile(&typeenv, &termenv)?;
-    Ok(automata)
+    let codegen = codegen::Codegen::compile(&typeenv, &termenv)?;
+    codegen.generate_rust()
 }
diff --git a/cranelift/isle/src/error.rs b/cranelift/isle/src/error.rs
index 2399fb1231..7fce2df669 100644
--- a/cranelift/isle/src/error.rs
+++ b/cranelift/isle/src/error.rs
@@ -11,6 +11,8 @@ pub enum Error {
     SemaError(#[from] SemaError),
     #[error("IO error")]
     IoError(#[from] std::io::Error),
+    #[error("Formatting error")]
+    FmtError(#[from] std::fmt::Error),
 }
 
 #[derive(Clone, Debug, Error)]
diff --git a/cranelift/isle/src/main.rs b/cranelift/isle/src/main.rs
index 922afbb57e..038a8a7a85 100644
--- a/cranelift/isle/src/main.rs
+++ b/cranelift/isle/src/main.rs
@@ -18,7 +18,7 @@ fn main() -> Result<(), error::Error> {
     stdin().read_to_string(&mut input)?;
     let mut parser = parser::Parser::new("<stdin>", &input[..]);
     let defs = parser.parse_defs()?;
-    let automata = compile::compile(&defs)?;
-    println!("automata: {:?}", automata);
+    let code = compile::compile(&defs)?;
+    println!("{}", code);
     Ok(())
 }