Don't generalize a rec. group, if any members are marked as monomorphic.

Fixes #607

src/Cryptol/TypeCheck/Infer.hs

@@ -642,7 +642,10 @@ inferCArm armNum (m : ms) =
      return (m1 : ms', Map.insertWith (\_ old -> old) x t ds, tMul n n')
 
 -- | @inferBinds isTopLevel isRec binds@ performs inference for a
--- strongly-connected component of 'P.Bind's. If @isTopLevel@ is true,
+-- strongly-connected component of 'P.Bind's.
+-- If any of the members of the recursive group are already marked
+-- as monomorphic, then we don't do generalzation.
+-- If @isTopLevel@ is true,
 -- any bindings without type signatures will be generalized. If it is
 -- false, and the mono-binds flag is enabled, no bindings without type
 -- signatures will be generalized, but bindings with signatures will
@@ -653,12 +656,11 @@ inferBinds isTopLevel isRec binds =
      -- declarations, mark all bindings lacking signatures as monomorphic
      monoBinds <- getMonoBinds
      let (sigs,noSigs) = partition (isJust . P.bSignature) binds
-         monos         = [ b { P.bMono = True } | b <- noSigs ]
-         binds' | monoBinds && not isTopLevel = sigs ++ monos
+         monos         = sigs ++ [ b { P.bMono = True } | b <- noSigs ]
+         binds' | any P.bMono binds           = monos
+                | monoBinds && not isTopLevel = monos
                 | otherwise                   = binds
 
-
-
          check exprMap =
         {- Guess type is here, because while we check user supplied signatures
            we may generate additional constraints. For example, `x - y` would

tests/issues/issue607.icry

@@ -0,0 +1,3 @@
+let (x,y)=(0,x+1)
+x
+y

tests/issues/issue607.icry.stdout

@@ -0,0 +1,5 @@
+Loading module Cryptol
+[warning] at <interactive>:1:5--1:18:
+  Defaulting the type of '<interactive>::y' to [1]
+0x0
+0x1