Use coerce instead of unsafeCoerce where appropriate (#130)

* Replace unsafeCoerce with safer alternative where possible

* Remove unused import

* Add docs to the Internal module and NonEmptyString constructor

* Remove 'usage of this constructor...' sentence

* Move constructor docs to type docs

Constructor docs don't yet appear in the generated documentation

* Add backticks around NonEmptyString in docs

* Add "For internal use only. Do not export" above to/fromNEString & listS

src/Data/String/NonEmpty/CodePoints.purs

@@ -33,19 +33,21 @@ import Data.Semigroup.Foldable (class Foldable1)
 import Data.Semigroup.Foldable as F1
 import Data.String.CodePoints (CodePoint)
 import Data.String.CodePoints as CP
-import Data.String.NonEmpty.Internal (NonEmptyString, fromString)
+import Data.String.NonEmpty.Internal (NonEmptyString(..), fromString)
 import Data.String.Pattern (Pattern)
 import Partial.Unsafe (unsafePartial)
-import Unsafe.Coerce (unsafeCoerce)
 
+-- For internal use only. Do not export.
 toNonEmptyString :: String -> NonEmptyString
-toNonEmptyString = unsafeCoerce
+toNonEmptyString = NonEmptyString
 
+-- For internal use only. Do not export.
 fromNonEmptyString :: NonEmptyString -> String
-fromNonEmptyString = unsafeCoerce
+fromNonEmptyString (NonEmptyString s) = s
 
+-- For internal use only. Do not export.
 liftS :: forall r. (String -> r) -> NonEmptyString -> r
-liftS = unsafeCoerce
+liftS f (NonEmptyString s) = f s
 
 fromCodePointArray :: Array CodePoint -> Maybe NonEmptyString
 fromCodePointArray = case _ of

src/Data/String/NonEmpty/CodeUnits.purs

@@ -33,20 +33,23 @@ import Data.Maybe (Maybe(..), fromJust)
 import Data.Semigroup.Foldable (class Foldable1)
 import Data.Semigroup.Foldable as F1
 import Data.String.CodeUnits as CU
-import Data.String.NonEmpty.Internal (NonEmptyString, fromString)
+import Data.String.NonEmpty.Internal (NonEmptyString(..), fromString)
 import Data.String.Pattern (Pattern)
 import Data.String.Unsafe as U
 import Partial.Unsafe (unsafePartial)
 import Unsafe.Coerce (unsafeCoerce)
 
+-- For internal use only. Do not export.
 toNonEmptyString :: String -> NonEmptyString
-toNonEmptyString = unsafeCoerce
+toNonEmptyString = NonEmptyString
 
+-- For internal use only. Do not export.
 fromNonEmptyString :: NonEmptyString -> String
-fromNonEmptyString = unsafeCoerce
+fromNonEmptyString (NonEmptyString s) = s
 
+-- For internal use only. Do not export.
 liftS :: forall r. (String -> r) -> NonEmptyString -> r
-liftS = unsafeCoerce
+liftS f (NonEmptyString s) = f s
 
 -- | Creates a `NonEmptyString` from a character array `String`, returning
 -- | `Nothing` if the input is empty.

src/Data/String/NonEmpty/Internal.purs

@@ -1,3 +1,9 @@
+-- | While most of the code in this module is safe, this module does
+-- | export a few partial functions and the `NonEmptyString` constructor.
+-- | While the partial functions are obvious from the `Partial` constraint in
+-- | their type signature, the `NonEmptyString` constructor can be overlooked
+-- | when searching for issues in one's code. See the constructor's
+-- | documentation for more information.
 module Data.String.NonEmpty.Internal where
 
 import Prelude
@@ -13,6 +19,12 @@ import Prim.TypeError as TE
 import Unsafe.Coerce (unsafeCoerce)
 
 -- | A string that is known not to be empty.
+-- |
+-- | You can use this constructor to create a `NonEmptyString` that isn't
+-- | non-empty, breaking the guarantee behind this newtype. It is
+-- | provided as an escape hatch mainly for the `Data.NonEmpty.CodeUnits`
+-- | and `Data.NonEmpty.CodePoints` modules. Use this at your own risk
+-- | when you know what you are doing.
 newtype NonEmptyString = NonEmptyString String
 
 derive newtype instance eqNonEmptyString ∷ Eq NonEmptyString