diff --git a/fine/src/parser.rs b/fine/src/parser.rs
index 802657ad..13cdd620 100644
--- a/fine/src/parser.rs
+++ b/fine/src/parser.rs
@@ -120,7 +120,7 @@ impl<'a> std::ops::IndexMut<TreeRef> for SyntaxTree<'a> {
 pub enum TreeKind {
     Error,
     File,
-    FunDecl,
+    FunctionDecl,
     ParamList,
     Parameter,
     TypeExpression,
@@ -488,7 +488,7 @@ fn function(p: &mut CParser) {
         block(p);
     }
 
-    p.end(m, TreeKind::FunDecl);
+    p.end(m, TreeKind::FunctionDecl);
 }
 
 fn param_list(p: &mut CParser) {
diff --git a/fine/src/semantics.rs b/fine/src/semantics.rs
index 40138628..af3a4598 100644
--- a/fine/src/semantics.rs
+++ b/fine/src/semantics.rs
@@ -369,6 +369,7 @@ impl<'a> Semantics<'a> {
 
         let result = match tree.kind {
             TreeKind::LetStatement => self.environment_of_let(parent, tree),
+            TreeKind::FunctionDecl => self.environment_of_func(parent, tree),
 
             // TODO: MORE Things that introduce an environment!
             _ => parent,
@@ -404,6 +405,44 @@ impl<'a> Semantics<'a> {
         EnvironmentRef::new(environment)
     }
 
+    fn environment_of_func(&self, parent: EnvironmentRef, tree: &Tree) -> EnvironmentRef {
+        let Some(param_list) = tree.nth_tree(2) else {
+            return parent; // SE
+        };
+        let param_list = &self.syntax_tree[param_list];
+        if param_list.kind != TreeKind::ParamList {
+            return parent; // SE
+        }
+
+        let mut environment = Environment::new(Some(parent));
+        for child in param_list.children.iter() {
+            let Child::Tree(ct) = child else {
+                continue;
+            };
+            let param = &self.syntax_tree[*ct];
+            if param.kind != TreeKind::Parameter {
+                continue;
+            }
+
+            let Some(param_name) = param.nth_token(0) else {
+                continue;
+            };
+
+            let declaration_type = if let Some(type_expression) = param.nth_tree(2) {
+                self.type_of(type_expression)
+                    .expect("the type expression should yield *some* type here")
+            } else {
+                Type::Error
+            };
+
+            environment
+                .declarations
+                .insert(param_name.as_str().into(), Declaration { declaration_type });
+        }
+
+        EnvironmentRef::new(environment)
+    }
+
     pub fn type_of(&self, t: TreeRef) -> Option<Type> {
         match self.types.borrow().get(&t) {
             None => (),
@@ -553,7 +592,16 @@ impl<'a> Semantics<'a> {
 
     fn type_of_type_expr(&self, tree: &Tree) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::TypeExpression);
-        Some(Type::Error)
+
+        // TODO: This will *clearly* need to get better.
+        let token = tree.nth_token(0)?;
+        match token.as_str() {
+            "f64" => Some(Type::F64),
+            "string" => Some(Type::String),
+            "bool" => Some(Type::Bool),
+            "()" => Some(Type::Nothing),
+            _ => Some(Type::Error),
+        }
     }
 
     fn type_of_block(&self, tree: &Tree) -> Option<Type> {
diff --git a/fine/tests/expression/argument.fine b/fine/tests/expression/argument.fine
new file mode 100644
index 00000000..bf9de0b8
--- /dev/null
+++ b/fine/tests/expression/argument.fine
@@ -0,0 +1,30 @@
+// @concrete:
+// | File
+// |   FunctionDecl
+// |     Fun:'"fun"'
+// |     Identifier:'"foo"'
+// |     ParamList
+// |       LeftParen:'"("'
+// |       Parameter
+// |         Identifier:'"x"'
+// |         Colon:'":"'
+// |         TypeExpression
+// |           Identifier:'"f64"'
+// |       RightParen:'")"'
+// |     Block
+// |       LeftBrace:'"{"'
+// |       ExpressionStatement
+// |         BinaryExpression
+// |           Identifier
+// |             Identifier:'"x"'
+// |           Plus:'"+"'
+// |           LiteralExpression
+// |             Number:'"7"'
+// |       RightBrace:'"}"'
+// |
+
+fun foo(x: f64) {
+  x + 7
+}
+
+// @type: 613 f64