diff --git a/fine/src/lib.rs b/fine/src/lib.rs
index d36953aa..d1eb8b8d 100644
--- a/fine/src/lib.rs
+++ b/fine/src/lib.rs
@@ -1,4 +1,32 @@
+use std::fs;
+
+use parser::parse;
+use semantics::{check, Semantics};
+
 pub mod compiler;
 pub mod parser;
 pub mod semantics;
 pub mod tokens;
+pub mod vm;
+
+pub fn process_file(file: &str) {
+    let source = match fs::read_to_string(file) {
+        Ok(c) => c,
+        Err(e) => {
+            eprintln!("Unable to read file {file}: {e}");
+            return;
+        }
+    };
+
+    // What am I doing here?
+    let (tree, lines) = parse(&source);
+    let semantics = Semantics::new(&tree, &lines);
+    check(&semantics);
+
+    // OK now there might be errors.
+    let mut errors = semantics.snapshot_errors();
+    errors.reverse();
+    for e in errors {
+        eprintln!("{file}: {}:{}: {}", e.start.0, e.start.1, e.message);
+    }
+}
diff --git a/fine/src/main.rs b/fine/src/main.rs
index 62c9b484..8d85e4b7 100644
--- a/fine/src/main.rs
+++ b/fine/src/main.rs
@@ -1,37 +1,8 @@
-use fine::parser::parse;
-use fine::semantics::Semantics;
 use std::env;
-use std::fs;
-
-pub fn process_file(file: &str) {
-    let source = match fs::read_to_string(file) {
-        Ok(c) => c,
-        Err(e) => {
-            eprintln!("Unable to read file {file}: {e}");
-            return;
-        }
-    };
-
-    // What am I doing here?
-    let (tree, lines) = parse(&source);
-    let semantics = Semantics::new(&tree, &lines);
-
-    // This is... probably wrong, I don't know, what am I doing?
-    for t in tree.trees() {
-        let _ = semantics.type_of(t);
-    }
-
-    // OK now there might be errors.
-    let mut errors = semantics.snapshot_errors();
-    errors.reverse();
-    for e in errors {
-        eprintln!("{file}: {}:{}: {}", e.start.0, e.start.1, e.message);
-    }
-}
 
 pub fn main() {
     let args: Vec<String> = env::args().collect();
     for arg in &args[1..] {
-        process_file(arg);
+        fine::process_file(arg);
     }
 }
diff --git a/fine/src/semantics.rs b/fine/src/semantics.rs
index 77de0afa..d9ef011b 100644
--- a/fine/src/semantics.rs
+++ b/fine/src/semantics.rs
@@ -841,6 +841,44 @@ impl<'a> Semantics<'a> {
     }
 }
 
+pub fn check(s: &Semantics) {
+    for t in s.syntax_tree.trees() {
+        let tree = &s.syntax_tree[t];
+        match tree.kind {
+            TreeKind::Error => {} // already reported
+            TreeKind::File => {}
+            TreeKind::FunctionDecl => {
+                let _ = s.environment_of(t);
+            }
+            TreeKind::ParamList => {}
+            TreeKind::Parameter => {}
+            TreeKind::TypeExpression => {
+                let _ = s.type_of_type_expr(tree);
+            }
+            TreeKind::Block => {
+                let _ = s.type_of_block(tree);
+            }
+            TreeKind::LetStatement => {
+                let _ = s.environment_of(t);
+            }
+            TreeKind::ReturnStatement => {}
+            TreeKind::ExpressionStatement
+            | TreeKind::LiteralExpression
+            | TreeKind::GroupingExpression
+            | TreeKind::UnaryExpression
+            | TreeKind::ConditionalExpression
+            | TreeKind::CallExpression
+            | TreeKind::BinaryExpression => {
+                let _ = s.type_of(t);
+            }
+            TreeKind::ArgumentList => {}
+            TreeKind::Argument => {}
+            TreeKind::IfStatement => {}
+            TreeKind::Identifier => {}
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;