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Update TypeMismatch for multiple possible types. #41

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Update TypeMismatch for multiple possible types. #41

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db152b5
Update TypeMismatch for multiple possible types.
bsermons Jul 8, 2016
d138a30
Fix ForeignError Show instance.
bsermons Jul 11, 2016
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28 changes: 19 additions & 9 deletions src/Data/Foreign.purs
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Expand Up @@ -44,16 +44,16 @@ foreign import data Foreign :: *

-- | A type for runtime type errors
data ForeignError
= TypeMismatch String String
= TypeMismatch (Array String) String
| ErrorAtIndex Int ForeignError
| ErrorAtProperty String ForeignError
| JSONError String

instance showForeignError :: Show ForeignError where
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While we're breaking things here, we should make this into a valid Show instance, and move this into a renderForeignError function.

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I'm not sure I understand, what makes this an invalid Show instance?

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There's an informal rule that Show should print purescript code, so like "(TypeMismatch " <> show exp <> show act <> ")" style, for each case.

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Ah I see, thanks.

show (TypeMismatch exp act) = "Type mismatch: expected " <> exp <> ", found " <> act
show (ErrorAtIndex i e) = "Error at array index " <> show i <> ": " <> show e
show (ErrorAtProperty prop e) = "Error at property " <> show prop <> ": " <> show e
show (JSONError s) = "JSON error: " <> s
show (ErrorAtIndex i e) = "(ErrorAtIndex " <> show i <> " " <> show e <> ")"
show (ErrorAtProperty prop e) = "(ErrorAtProperty " <> show prop <> " " <> show e <> ")"
show (JSONError s) = "(JSONError " <> show s <> ")"
show (TypeMismatch exps act) = "(TypeMismatch " <> show exps <> " " <> show act <> ")"

instance eqForeignError :: Eq ForeignError where
eq (TypeMismatch a b) (TypeMismatch a' b') = a == a' && b == b'
Expand All @@ -62,6 +62,16 @@ instance eqForeignError :: Eq ForeignError where
eq (JSONError s) (JSONError s') = s == s'
eq _ _ = false

renderForeignError :: ForeignError -> String
renderForeignError (ErrorAtIndex i e) = "Error at array index " <> show i <> ": " <> show e
renderForeignError (ErrorAtProperty prop e) = "Error at property " <> show prop <> ": " <> show e
renderForeignError (JSONError s) = "JSON error: " <> s
renderForeignError (TypeMismatch exps act) = "Type mismatch: expected " <> to_s exps <> ", found " <> act
where
to_s [] = "???"
to_s [typ] = typ
to_s typs = "one of " <> show typs

-- | An error monad, used in this library to encode possible failure when
-- | dealing with foreign data.
type F = Either ForeignError
Expand Down Expand Up @@ -90,7 +100,7 @@ foreign import tagOf :: Foreign -> String
-- | value.
unsafeReadTagged :: forall a. String -> Foreign -> F a
unsafeReadTagged tag value | tagOf value == tag = pure (unsafeFromForeign value)
unsafeReadTagged tag value = Left (TypeMismatch tag (tagOf value))
unsafeReadTagged tag value = Left (TypeMismatch [tag] (tagOf value))

-- | Test whether a foreign value is null
foreign import isNull :: Foreign -> Boolean
Expand All @@ -113,7 +123,7 @@ readChar value = either (const error) fromString (readString value)
fromString = maybe error pure <<< toChar

error :: F Char
error = Left $ TypeMismatch "Char" (tagOf value)
error = Left $ TypeMismatch ["Char"] (tagOf value)

-- | Attempt to coerce a foreign value to a `Boolean`.
readBoolean :: Foreign -> F Boolean
Expand All @@ -131,9 +141,9 @@ readInt value = either (const error) fromNumber (readNumber value)
fromNumber = maybe error pure <<< Int.fromNumber

error :: F Int
error = Left $ TypeMismatch "Int" (tagOf value)
error = Left $ TypeMismatch ["Int"] (tagOf value)

-- | Attempt to coerce a foreign value to an array.
readArray :: Foreign -> F (Array Foreign)
readArray value | isArray value = pure $ unsafeFromForeign value
readArray value = Left (TypeMismatch "array" (tagOf value))
readArray value = Left (TypeMismatch ["array"] (tagOf value))
2 changes: 1 addition & 1 deletion src/Data/Foreign/Index.purs
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Expand Up @@ -31,7 +31,7 @@ infixl 9 ix as !
foreign import unsafeReadPropImpl :: forall r k. Fn4 r (Foreign -> r) k Foreign (F Foreign)

unsafeReadProp :: forall k. k -> Foreign -> F Foreign
unsafeReadProp k value = runFn4 unsafeReadPropImpl (Left (TypeMismatch "object" (typeOf value))) pure k value
unsafeReadProp k value = runFn4 unsafeReadPropImpl (Left (TypeMismatch ["object"] (typeOf value))) pure k value

-- | Attempt to read a value from a foreign value property
prop :: String -> Foreign -> F Foreign
Expand Down
6 changes: 3 additions & 3 deletions src/Data/Foreign/Keys.purs
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Expand Up @@ -14,7 +14,7 @@ foreign import unsafeKeys :: Foreign -> Array String

-- | Get an array of the properties defined on a foreign value
keys :: Foreign -> F (Array String)
keys value | isNull value = Left $ TypeMismatch "object" "null"
keys value | isUndefined value = Left $ TypeMismatch "object" "undefined"
keys value | isNull value = Left $ TypeMismatch ["object"] "null"
keys value | isUndefined value = Left $ TypeMismatch ["object"] "undefined"
keys value | typeOf value == "object" = Right $ unsafeKeys value
keys value = Left $ TypeMismatch "object" (typeOf value)
keys value = Left $ TypeMismatch ["object"] (typeOf value)