Allow where defs to refer to themselves

src/Lib/Types.idr

@@ -101,6 +101,8 @@ data Tm : Type where
   Case : FC -> Tm -> List CaseAlt -> Tm
   -- need type?
   Let : FC -> Name -> Tm -> Tm -> Tm
+  -- for desugaring where
+  LetRec : FC -> Name -> Tm -> Tm -> Tm
   Lit : FC -> Literal -> Tm
 
 %name Tm t, u, v
@@ -117,6 +119,7 @@ HasFC Tm where
   getFC (Case fc t xs) = fc
   getFC (Lit fc _) = fc
   getFC (Let fc _ _ _) = fc
+  getFC (LetRec fc _ _ _) = fc
 
 covering
 Show Tm
@@ -141,6 +144,7 @@ Show Tm where
   show (Pi _ str Auto t u) = "(Pi {{\{str} : \{show t}}} => \{show u})"
   show (Case _ sc alts) = "(Case \{show sc} \{show alts})"
   show (Let _ nm t u) = "(Let \{nm} \{show t} \{show u})"
+  show (LetRec _ nm t u) = "(LetRec \{nm} \{show t} \{show u})"
 
 public export
 showTm : Tm -> String
@@ -214,6 +218,7 @@ pprint names tm = go 0 names tm
     go p names (Case _ sc alts) = parens 0 p $ text "case" <+> go 0 names sc <+> text "of" ++ (nest 2 (line ++ stack (map (goAlt 0 names) alts)))
     go p names (Lit _ lit) = text (show lit)
     go p names (Let _ nm t u) = parens 0 p $ text "let" <+> text nm <+> ":=" <+> go 0 names t <+> "in" </> (nest 2 $ go 0 (nm :: names) u)
+    go p names (LetRec _ nm t u) = parens 0 p $ text "letrec" <+> text nm <+> ":=" <+> go 0 names t <+> "in" </> (nest 2 $ go 0 (nm :: names) u)
 
 data Val : Type
 
@@ -246,6 +251,7 @@ data Val : Type where
   VLam : FC -> Name -> Closure -> Val
   VPi : FC -> Name -> Icit -> (a : Lazy Val) -> (b : Closure) -> Val
   VLet : FC -> Name -> Val -> Val -> Val
+  VLetRec : FC -> Name -> Val -> Val -> Val
   VU : FC -> Val
   VLit : FC -> Literal -> Val
 
@@ -260,6 +266,7 @@ getValFC (VPi fc _ _ a b) = fc
 getValFC (VU fc) = fc
 getValFC (VLit fc _) = fc
 getValFC (VLet fc _ _ _) = fc
+getValFC (VLetRec fc _ _ _) = fc
 
 
 public export
@@ -281,6 +288,7 @@ Show Val where
   show (VU _) = "U"
   show (VLit _ lit) = show lit
   show (VLet _ nm a b) = "(%let \{show nm} = \{show a} in \{show b}"
+  show (VLetRec _ nm a b) = "(%letrec \{show nm} = \{show a} in \{show b}"
 
 public export
 Env : Type