903973d · elk · git.iko.soy

git.iko.soy/elk

on master help sign in

Improve explanation on infinite type aliases

903973dEvan Czaplicki12 years ago

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

compare with master

unifiedsplit

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

1{-# OPTIONS_GHC -Wall #-}

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

2+module Transform.Canonicalize.Setup

3+ ( environment

4+ , typeAliasErrorSegue

5+ , typeAliasErrorExplanation

6+ ) where

4import Control.Arrow (first)

8import Control.Arrow (first)

5import Control.Monad (foldM)

9import Control.Monad (foldM)

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

178 aliases ->

182 aliases ->

179 throwError

183 throwError

180 [ P.vcat

184 [ P.vcat

181− [ P.text (eightyCharLines 0 msg1)

185+ [ P.text (eightyCharLines 0 mutuallyRecursiveMessage)

182 , indented (map typeAlias aliases)

186 , indented (map typeAlias aliases)

183− , P.text (eightyCharLines 0 msg2)

187+ , P.text (eightyCharLines 0 typeAliasErrorSegue)

184 , indented (map datatype aliases)

188 , indented (map datatype aliases)

185− , P.text (eightyCharLines 0 msg3)

189+ , P.text (eightyCharLines 0 typeAliasErrorExplanation)

186 ]

190 ]

187 ]

191 ]

188

192

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

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

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

208

212

209

213

210−msg1 :: String

214+mutuallyRecursiveMessage :: String

215+mutuallyRecursiveMessage =

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

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

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

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

213

218

214−msg2 :: String

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

216

219

217−msg3 :: String

220+typeAliasErrorSegue :: String

218−msg3 =

221+typeAliasErrorSegue =

222+ "Try this instead:"

223+

224+

225+typeAliasErrorExplanation :: String

226+typeAliasErrorExplanation =

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

227+ "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 \

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

221− \it during type inference."

229+ \expanding it during type inference."

222

230

223

231

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

232-- 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

12import qualified AST.Type as T

13import qualified AST.Variable as Var

14import qualified Transform.Expression as Expr

15+import qualified Transform.Canonicalize.Setup as Setup

16import AST.PrettyPrint

17import AST.PrettyPrint

17import Elm.Utils ((|>))

18import Elm.Utils ((|>))

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

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

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

163

164

164 report name args tipe =

165 report name args tipe =

166+ P.vcat

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

167+ [ P.text $ eightyCharLines 0 msg1

166− , indented $ D.TypeAlias name args tipe

168+ , indented $ D.TypeAlias name args tipe

167− , P.text $ eightyCharLines 0 msg2

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

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

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

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

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

170− ]

172+ ]

171 where

173 where

174+ msg1 =

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

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

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

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

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

177+ \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."