Parsing FParsec-解析器序列
假设我有一些文字:Parsing FParsec-解析器序列,parsing,f#,fparsec,Parsing,F#,Fparsec,假设我有一些文字: a = "foobarbaz" b = "foobar" c = "foo" d = "rubbish" e = "foobazbar" 以及分别用于字符串“foo”、“bar”和“baz”的三个解析器foo、bar和baz 我将如何创建一个解析器来提供结果: a = ["foo", "bar", "baz"] b = ["foo", "bar"] c = ["foo"] d = [] e = ["foo"] 当针对上述输入运行时?基本上,在构建列表时,尝试每种可能性直到
a = "foobarbaz"
b = "foobar"
c = "foo"
d = "rubbish"
e = "foobazbar"
以及分别用于字符串“foo”、“bar”和“baz”的三个解析器foo、bar和baz
我将如何创建一个解析器来提供结果:
a = ["foo", "bar", "baz"]
b = ["foo", "bar"]
c = ["foo"]
d = []
e = ["foo"]
当针对上述输入运行时?基本上,在构建列表时,尝试每种可能性直到失败。我可以使用用户状态,但如果可能,我希望避免使用。(我想让各个解析器自己不知道用户状态)
我得到的最接近的结果如下:
let foo = pstring "foo"
let bar = pstring "bar"
let baz = pstring "baz"
let foobar = pipe2 foo bar Seq.of2
let foobarbaz = pipe3 foo bar baz Seq.of3
let fooseq = choice (Seq.map attempt [foobarbaz; foobar; foo |>> Seq.of1 ;])
//(the Seq.ofx functions just take arguments and create a sequence of them)
在我看来,一定有更好的方法可以做到这一点?FParsec没有内置的序列组合器,它完全可以满足您的要求,但您可以自己实现一个,如以下示例所示:
let mySeq (parsers: seq<Parser<'t,'u>>) : Parser<'t[],'u> =
let ps = Array.ofSeq parsers
if ps.Length = 0 then preturn [||]
else
fun stream ->
let mutable stateTag = stream.StateTag
let mutable reply = ps.[0] stream
let mutable error = reply.Error
let mutable myReply = Reply()
if reply.Status <> Ok then myReply.Result <- [||]
else
// create array to hold results
let mutable xs = Array.zeroCreate ps.Length
xs.[0] <- reply.Result
let mutable i = 1
while i < ps.Length do
stateTag <- stream.StateTag
reply <- ps.[i] stream
error <- if stateTag <> stream.StateTag then reply.Error
else mergeErrors error reply.Error
if reply.Status = Ok then
xs.[i] <- reply.Result
i <- i + 1
else // truncate array and break loop
xs <- Array.sub xs 0 i
i <- ps.Length
myReply.Result <- xs
myReply.Status <- if reply.Status = Error && stateTag = stream.StateTag
then Ok
else reply.Status
myReply.Error <- error
myReply
let fooSeq = mySeq [foo; bar; baz]