Measure size of AST

towards #866

src/Swarm/Language/Syntax.hs

@@ -71,6 +71,7 @@ module Swarm.Language.Syntax (
   fvT,
   fv,
   mapFree1,
+  measureAstSize,
 ) where
 
 import Control.Arrow (Arrow ((&&&)))
@@ -965,3 +966,17 @@ mapFree1 x f = fvT %~ (\t -> if t == TVar x then f t else t)
 
 lowShow :: Show a => a -> Text
 lowShow a = toLower (from (show a))
+
+-- | Note that the size constants for the recursive constructors
+-- are somewhat arbitrary; perhaps we should take into account
+-- the other fields of those constructors.
+measureAstSize :: Term -> Int
+measureAstSize = \case
+  SLam _ _ (Syntax _ t1) -> 2 + measureAstSize t1
+  SApp (Syntax _ t1) (Syntax _ t2) -> measureAstSize t1 + measureAstSize t2
+  SLet _ _ _ (Syntax _ t1) (Syntax _ t2) -> 2 + measureAstSize t1 + measureAstSize t2
+  SPair (Syntax _ t1) (Syntax _ t2) -> measureAstSize t1 + measureAstSize t2
+  SDef _ _ _ (Syntax _ t1) -> 2 + measureAstSize t1
+  SBind _ (Syntax _ t1) (Syntax _ t2) -> 1 + measureAstSize t1 + measureAstSize t2
+  SDelay _ (Syntax _ t1) -> 1 + measureAstSize t1
+  _ -> 1