Nix.Builtins: replaceStrings: m refactor: mv funcs to local scope

Author: Anton-Latukha

src/Nix/Builtins.hs

@@ -938,27 +938,17 @@ replaceStrings
   -> NValue t f m
   -> NValue t f m
   -> m (NValue t f m)
--- `ns*` goes for NixString here, which are with context - remember
 replaceStrings tfrom tto ts =
-  fromValue (Deeper tfrom) >>= \(nsFrom :: [NixString]) ->
-  fromValue (Deeper tto)   >>= \(nsTo   :: [NixString]) ->
-  fromValue ts             >>= \(ns     ::  NixString ) ->
-    do
+  do
+      -- `ns*` goes for NixString here, which are with context - remember
+      (nsFrom :: [NixString]) <- fromValue (Deeper tfrom)
+      (nsTo   :: [NixString]) <- fromValue (Deeper tto)
+      (ns     ::  NixString ) <- fromValue ts
+
       when (length nsFrom /= length nsTo)
         $ throwError $ ErrorCall "builtins.replaceStrings: Arguments `from`&`to` are lists `from` what replace `to` what, so the number of their inhabitanting elements must always match."
       let
 
-        from = fmap stringIgnoreContext nsFrom
-
-        lookupPrefix s =
-          do  -- monadic context handles Maybe result here, aka if Nothing returned
-            (prefix, replacement) <- find ((`Text.isPrefixOf` s) . fst)
-              $ zip from nsTo
-            let rest = Text.drop (Text.length prefix) s
-            pure (prefix, replacement, rest)
-
-        finish = makeNixString . LazyText.toStrict . Builder.toLazyText
-
         go source resultAccum ctx =
           case lookupPrefix source of
             Nothing ->
@@ -976,6 +966,17 @@ replaceStrings tfrom tto ts =
               (finish result)
               (\(h, t) -> go t (result <> Builder.singleton h))
               (Text.uncons text)
+           where
+            finish = makeNixString . LazyText.toStrict . Builder.toLazyText
+
+          lookupPrefix src =
+            do  -- monadic context handles Maybe result here, aka if Nothing returned
+              (prefix, replacement) <- find ((`Text.isPrefixOf` src) . fst)
+                $ zip from nsTo
+              let rest = Text.drop (Text.length prefix) src
+              pure (prefix, replacement, rest)
+           where
+            from = fmap stringIgnoreContext nsFrom
 
       toValue
         $ go (stringIgnoreContext ns) mempty