我有以下代码行,当使用GHC编译时,它没有任何障碍:
addRDF c (Just (FILE)) = do
(_:file:_) <- getArgs
check <- doesFileExist file
if check then do rdfG <- TLI.readFile file >>= (return . parseN3fromText)
case rdfG of (Left s) -> putStrLn s
(Right g) -> storeRDF c g
else do putStrLn "Specified files does not exist"
但是当我在cabal构建过程中运行它时,它会转储出以下错误。
Repository/Adder.hs:46:35:
Unexpected semi-colons in conditional:
if check then do { rdfG <- TLI.readFile file
>>=
(return . parseN3fromText);
case rdfG of {
(Left s) -> putStrLn s
(Right g) -> storeRDF c g } }; else do { putStrLn
"Specified files does not exist" }
Perhaps you meant to use -XDoAndIfThenElse?
我可以在错误中看到额外的分号,但我不明白它的来源。
这是我的cabal配置文件:
cabal-version: >= 1.2
build-type: Simple
library
build-depends:
base,
containers,
HTTP >= 4000.2.2,
directory >= 1.1.0.0,
text >= 0.11.1.13,
swish >= 0.6.5.2
exposed-modules: Repository.Adder, Repository.Configuration
ghc-options: -Wall
executable repository-add
main-is: repository-add.hs
build-depends:
MissingH,
swish >= 0.6.5.2,
split >= 0.1.4.2
ghc-options: -Wall
更新
正确缩进if
:
addRDF c (Just (FILE)) = do (_:file:_) <- getArgs
check <- doesFileExist file
if check
then do rdfG <- TLI.readFile file >>= (return . parseN3fromText)
case rdfG of (Left s) -> putStrLn s
(Right g) -> storeRDF c g
else do putStrLn "Specified files does not exist"
我现在在check
之后得到一个分号:
Repository/Adder.hs:46:35:
Unexpected semi-colons in conditional:
if check; then do { rdfG <- TLI.readFile file
>>=
(return . parseN3fromText);
case rdfG of {
(Left s) -> putStrLn s
(Right g) -> storeRDF c g } }; else do { putStrLn
"Specified files does not exist" }
Perhaps you meant to use -XDoAndIfThenElse?
答案 0 :(得分:15)
您的缩进是不正确的,但是当您使用原始GHC编译器时它会起作用,因为它会自动打开错误消息(DoAndIfThenElse
)中提到的语法扩展。
在Cabal中,您必须指定手动使用的语言扩展名,位于代码文件的顶部或Cabal文件中;否则,编译器将不会启用它们。
if-clauses缩进的一个正确版本是这样的:
if check
then do
rdfG <- TLI.readFile file >>= (return . parseN3fromText)
case rdfG of
(Left s) -> putStrLn s
(Right g) -> storeRDF c g
else putStrLn "Specified files does not exist"
您必须将then
部分和else
部分保持在比它们所属的块更深的缩进级别。