app/Gyehoek/Scheme/Syntax.hs

@@ -40,10 +40,17 @@ data Lit
   | LitBool Bool
   deriving (Show, Generic)
 
+data Define
+  = DefineConstant Name Exp
+  | DefineProcedure Name (List Name) (List Exp)
+  deriving (Show, Generic)
+
 data Exp
   = ExpLet (NonEmpty (Name, Exp)) Exp
   | ExpPrim (Prim Exp)
   | ExpBegin (List Exp)
+  | ExpDefine Define
+  | ExpIf Exp Exp Exp
   | ExpLit Lit
   | ExpApply Exp (List Exp)
   | ExpLambda (List Name) Exp
@@ -78,17 +85,30 @@ instance SexpIso Lit where
     $ With (. sexpIso)
     $ End
 
+instance SexpIso Define where
+  sexpIso = match
+    $ With (. defconst)
+    $ With (. defun)
+    $ End
+    where
+      defconst = list $ el (sym "define") >>> el symbol >>> el sexpIso
+      defun = list $ el (sym "define") >>> el args >>> rest sexpIso
+      args = list $ el symbol >>> rest symbol
+  
 instance SexpIso Exp where
   sexpIso = match
     $ With (. Gyehoek.Sexp.let_ symbol sexpIso sexpIso)
     $ With (. sexpIso)
     $ With (\bgn -> bgn . list (el (sym "begin") >>> rest sexpIso))
     $ With (. sexpIso)
+    $ With (. if_)
+    $ With (. sexpIso)
     $ With (\app -> app . list (el sexpIso >>> rest sexpIso))
     $ With (. lam)
     $ With (. symbol)
     $ End
     where
+      if_ = list $ el (sym "if") >>> el sexpIso >>> el sexpIso >>> el sexpIso
       lam = list
         ( el (sym "lambda")
           >>> el (sexpIso @(List Name))