diff --git a/src/main.rs b/src/main.rs
index 7e686ea..01c2d7b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -167,8 +167,10 @@ pub fn run(src: &'static str) {
 
 pub fn main() {
     let src = "
-box foo = 42
-foo
+match foo with {
+    :a -> :b
+    :c -> :d
+}
     ";
     run(src);
     // struct_scalpel::print_dissection_info::<value::Value>()
diff --git a/src/validator.rs b/src/validator.rs
index 0f30a9f..d9e737e 100644
--- a/src/validator.rs
+++ b/src/validator.rs
@@ -256,7 +256,41 @@ impl<'a> Validator<'a> {
             // check arity is 1 if first term is keyword
             // check arity against fn info if first term is word and second term is args
             Ast::Synthetic(first, second, rest) => {
-                todo!()
+                match (&first.0, &second.0) {
+                    (Ast::Word(_), Ast::Keyword(_)) => {
+                        let (expr, span) = first.as_ref();
+                        self.ast = expr;
+                        self.span = *span;
+                        self.validate();
+                    }
+                    (Ast::Keyword(_), Ast::Arguments(args)) => {
+                        if args.len() != 1 {
+                            self.err("called keywords may only take one argument".to_string())
+                        }
+                        let (expr, span) = second.as_ref();
+                        self.ast = expr;
+                        self.span = *span;
+                        self.validate();
+                    }
+                    (Ast::Word(_), Ast::Arguments(_)) => {
+                        let (expr, span) = first.as_ref();
+                        self.ast = expr;
+                        self.span = *span;
+                        self.validate();
+
+                        let (expr, span) = second.as_ref();
+                        self.ast = expr;
+                        self.span = *span;
+                        self.validate();
+                    }
+                    _ => unreachable!(),
+                }
+                for term in rest {
+                    let (expr, span) = term;
+                    self.ast = expr;
+                    self.span = *span;
+                    self.validate();
+                }
             }
             Ast::When(clauses) => {
                 // let tailpos = self.status.tail_position;