1 files changed, 23 insertions, 9 deletions
diff --git a/src/node.rs b/src/node.rs
index b63270e..a279eb9 100644
--- a/src/node.rs
+++ b/src/node.rs
@@ -8,6 +8,7 @@ use crate::types::{Type, TypeSignature};
 #[derive(Debug, Copy, Clone)]
 pub enum CompileError {
     MissingArguments,
+    InvalidArguments,
     Codegen(fmt::Error),
 }
 
@@ -18,26 +19,39 @@ impl From<fmt::Error> for CompileError {
 }
 
 /// an instantiable Node, parametrized by its connected input types
+pub const MAX_INPUTS: usize = 16;
+
 #[enum_dispatch]
 pub trait ConcreteNode {
-    fn max_inputs(&self) -> usize;
-    fn num_inputs(&self, _connected: &[Option<Type>]) -> usize {
-        self.max_inputs()
-    }
-
-    // set of possible input type combinations given current connections
-    fn signatures_matching(&self, connected: &[Option<Type>]) -> Vec<TypeSignature>;
+    /// given the current connections, which inputs are available?
+    ///
+    /// This can return more inputs than those connected, indicating missing or optional connections.
+    /// This must not fail but fallback to a default signature that allows connections to be made.
+    fn visible_inputs(&self, connected: &[Option<Type>; MAX_INPUTS]) -> Vec<Option<Type>>;
 
-    fn signature(&self, connected: &[Option<Type>]) -> TypeSignature;
+    /// given the current connections, what is this node's signature?
+    ///
+    /// This determines the output types shown and is used for compilation. If no valid signature corresponds
+    /// to the set of inputs, this must fail. If the implementation accepts optional inputs, it may validate
+    /// them here or leave that to be done in `compile`.
+    fn signature(
+        &self,
+        connected: &[Option<Type>; MAX_INPUTS],
+    ) -> Result<TypeSignature, CompileError>;
 
+    /// generate code for this node.
+    ///
+    /// The number of `inputs` and `outputs` correspond to the types in `signature`.
+    /// This must fail if valid code can not be generated.
     fn compile(
         &self,
+        f: &mut dyn fmt::Write,
         signature: TypeSignature,
         inputs: Vec<Option<String>>,
         outputs: Vec<String>,
-        f: &mut dyn fmt::Write,
     ) -> Result<(), CompileError>;
 
+    /// optionaly render additional UI in the body of this node.
     fn show_body(&mut self, ui: &mut egui::Ui) -> egui::Response {
         ui.response()
     }