"Signal" is just [] without an empty constructor (i.e. a lazy corecursive stream). As far as your Haskell code is concerned, there is nothing special whatsoever

"Signal" is just [] without an empty constructor (i.e. a lazy corecursive stream). As far as your Haskell code is concerned, there is nothing special whatsoever about signals, and indeed it's just a normal data type until the Clash-specific Core layer kicks in. I think I mixed up "shallow" and "deep" embedding - by "deep embedding", I meant to say that there is no secondary AST manually defined for the embedded language, but I think that is actually a shallow embedding. Looks like I can't correct my earlier comment. Only the top level function has to be first order - you can use higher order functions within the body of your code.