903973d · elk · git.iko.soy

git.iko.soy/elk

Improve explanation on infinite type aliases

commit903973dcd57063756b78566db1b8c7de4bff7e02 authorEvan Czaplicki <info@elm-lang.org> dateSun 23 Nov 2014, 22:01 (12 years ago) parent393337f

2 files changed+34−28

compare with master

unifiedsplit

src/Transform/Canonicalize/Setup.hs+22−14 src/Transform/Check.hs+12−14

src/Transform/Canonicalize/Setup.hs+22−14

@@ -1,5 +1,9 @@

11{-# OPTIONS_GHC -Wall #-}

2−module Transform.Canonicalize.Setup (environment) where

2+module Transform.Canonicalize.Setup

3+ ( environment

4+ , typeAliasErrorSegue

5+ , typeAliasErrorExplanation

6+ ) where

48import Control.Arrow (first)

59import Control.Monad (foldM)

@@ -178,11 +182,11 @@ addTypeAlias moduleName env scc =

178182 aliases ->

179183 throwError

180184 [ P.vcat

181− [ P.text (eightyCharLines 0 msg1)

185+ [ P.text (eightyCharLines 0 mutuallyRecursiveMessage)

182186 , indented (map typeAlias aliases)

183− , P.text (eightyCharLines 0 msg2)

187+ , P.text (eightyCharLines 0 typeAliasErrorSegue)

184188 , indented (map datatype aliases)

185− , P.text (eightyCharLines 0 msg3)

189+ , P.text (eightyCharLines 0 typeAliasErrorExplanation)

186190 ]

187191 ]

188192

@@ -207,18 +211,22 @@ indented decls = P.vcat (map prty decls) <> P.text "\n"

207211 prty decl = P.text "\n " <> pretty decl

208212

209213

210−msg1 :: String

211−msg1 = "The following type aliases are mutually recursive, forming an \

212− \infinite type. When you expand them, they just keep getting bigger:"

214+mutuallyRecursiveMessage :: String

215+mutuallyRecursiveMessage =

216+ "The following type aliases are mutually recursive, forming an \

217+ \infinite type. When you expand them, they just keep getting bigger:"

213218

214−msg2 :: String

215−msg2 = "Instead, you can try something like this:"

216219

217−msg3 :: String

218−msg3 =

219− "It looks very similar, but the 'type' keyword creates a brand new type. \

220− \By giving the type an explicit name, we can avoid infinitely expanding \

221− \it during type inference."

220+typeAliasErrorSegue :: String

221+typeAliasErrorSegue =

222+ "Try this instead:"

223+

224+

225+typeAliasErrorExplanation :: String

226+typeAliasErrorExplanation =

227+ "It looks very similar, but the 'type' keyword creates a brand new type, \

228+ \not just an alias for an existing one. This lets us avoid infinitely \

229+ \expanding it during type inference."

222230

223231

224232-- When canonicalizing, all _values should be Local, but all _adts and _patterns

src/Transform/Check.hs+12−14

@@ -12,6 +12,7 @@ import qualified AST.Pattern as Pattern

1212import qualified AST.Type as T

1313import qualified AST.Variable as Var

1414import qualified Transform.Expression as Expr

15+import qualified Transform.Canonicalize.Setup as Setup

1516

1617import AST.PrettyPrint

1718import Elm.Utils ((|>))

@@ -162,18 +163,15 @@ infiniteTypeAliases decls =

162163 indented decl = P.text "\n " <> pretty decl <> P.text "\n"

163164

164165 report name args tipe =

165− P.vcat [ P.text $ eightyCharLines 0 msg1

166− , indented $ D.TypeAlias name args tipe

167− , P.text $ eightyCharLines 0 msg2

168− , indented $ D.Datatype name args [(name,[tipe])]

169− , P.text $ eightyCharLines 0 msg3 ++ "\n"

170− ]

166+ P.vcat

167+ [ P.text $ eightyCharLines 0 msg1

168+ , indented $ D.TypeAlias name args tipe

169+ , P.text $ eightyCharLines 0 Setup.typeAliasErrorSegue

170+ , indented $ D.Datatype name args [(name,[tipe])]

171+ , P.text $ eightyCharLines 0 Setup.typeAliasErrorExplanation ++ "\n"

172+ ]

171173 where

172− msg1 = "Type alias '" ++ name ++ "' is an infinite type. " ++

173− "Notice that it appears in its own definition, so when \

174− \you expand it, it just keeps getting bigger:"

175− msg2 = "Try this instead:"

176− msg3 = "It looks very similar, but an algebraic data type (ADT) \

177− \actually creates a new type. Unlike with a type alias, this \

178− \freshly created type is meaningful on its own, so an ADT \

179− \does not need to be expanded."

174+ msg1 =

175+ "Type alias '" ++ name ++ "' is an infinite type. " ++

176+ "Notice that it appears in its own definition, so when \

177+ \you expand it, it just keeps getting bigger:"