1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
|
<sect> <idx/GetOpt/
<label id="sec:GetOpt">
<p>
The <tt/GetOpt/ library contains Sven Panne's Haskell implementation
of <tt/getopt/, providing features nigh-on identical to GNU <tt/getopt/:
<tscreen><verb>
module GetOpt where
-- representing a single option:
data OptDescr a
= Option [Char] -- list of short option characters
[String] -- list of long option strings (without "--")
(ArgDescr a) -- argument descriptor
String -- explanation of option for user
-- argument option:
data ArgDescr a
= NoArg a -- no argument expected
| ReqArg (String -> a) String -- option requires argument
| OptArg (Maybe String -> a) String -- optional argument
usageInfo :: String -- header
-> [OptDescr a] -- options recognised
-> String -- nicely formatted decription of options
getOpt :: ArgOrder a -- non-option handling
-> [OptDescr a] -- options recognised
-> [String] -- the command-line
-> ( [a] -- options
, [String] -- non-options
,[String] -- error messages
)
data ArgOrder a
= RequireOrder
| Permute
| ReturnInOrder (String -> a)
</verb></tscreen>
<itemize>
<item> The command-line options recognised is described by a list of
<tt/OptDescr/ values. The <tt/OptDescr/ describes the long and short
strings that recognise the option, together with a help string and
info on whether the option takes extra arguments, if any.
<item>
From a list of option values, <tt/usageInfo/ returns a nicely
formatted string that enumerates the different options supported
together with a short message about what
<item>
To decode a command-line with respect to a list of options,
<tt/getOpt/ is used. It processes the command-line, and returns
the list of values that matched (and those that didn't). The first
argument to <tt/getOpt/ controls whether the user is to give the
options in any old order or not.
</itemize>
To hopefully illuminate the role of the different <tt/GetOpt/ data
structures, here's the command-line options for a (very simple)
compiler:
<tscreen><verb>
module Opts where
import GetOpt
import Maybe ( fromMaybe )
data Flag
= Verbose | Version
| Input String | Output String | LibDir String
deriving Show
options :: [OptDescr Flag]
options =
[ Option ['v'] ["verbose"] (NoArg Verbose) "chatty output on stderr"
, Option ['V','?'] ["version"] (NoArg Version) "show version number"
, Option ['o'] ["output"] (OptArg outp "FILE") "output FILE"
, Option ['c'] [] (OptArg inp "FILE") "input FILE"
, Option ['L'] ["libdir"] (ReqArg LibDir "DIR") "library directory"
]
inp,outp :: Maybe String -> Flag
outp = Output . fromMaybe "stdout"
inp = Input . fromMaybe "stdout"
compilerOpts :: [String] -> IO ([Flag], [String])
compilerOpts argv =
case (getOpt Permute options argv) of
(o,n,[] ) -> return (o,n)
(_,_,errs) -> fail (userError (concat errs ++ usageInfo header options))
where header = "Usage: ic [OPTION...] files..."
</verb></tscreen>
|
