Codec.Sexpr

A Sexpr is an S-expressionin the style of Rivest's Canonical S-expressions. Atoms may be of any type, but String and ByteString have special support. Rivest's implementation of S-expressions is unusual in supporting MIME type hints for each atom. See http:people.csail.mit.edurivestSexp.txt

Basics

data Sexpr s

Instances

Functor Sexpr

The Functor instance maps over the underlying atomic contents of the S-expression. It does not map only over the top-level list, but over the fringe.

Foldable Sexpr

Traversable Sexpr

Eq s => Eq (Sexpr s)

Read s => Read (Sexpr s)

Show (Sexpr String)

Show s => Show (Sexpr s)

Arbitrary a => Arbitrary (Sexpr a)

isAtom :: Sexpr a -> Bool

A predicate for identifying atoms, whether or not they have explicit hints.

isList :: Sexpr a -> Bool

A predicate for recognizing lists.

atom :: a -> Sexpr a

Construct an atom.

list :: [Sexpr a] -> Sexpr a

Construct a list.

unAtom :: Sexpr s -> s

Extract the content of an atom, discarding any MIME type hint.

unList :: Sexpr s -> [Sexpr s]

Extract the sub-S-expressions of a List. If all you intend to do is traverse or map over that list, the Functor instance of S-expressions may work just fine.

Hinted Atoms

hintedAtom :: String -> a -> Sexpr a

Construct an atom with a MIME type hint. hintedAtom defaultHint == atom

hint :: Sexpr a -> Maybe String

Extract the hint of an atom. Lists do not have hints, but all atoms have hints.

defaultHint :: String

Any atom whose hint is not specified is assumed to be text/plain; charset=iso-8859-1. This is that default value.

Character predicates to support encoding

isTokenChar :: Char -> Bool

Tokens may internally contain any of the characters legitimate to begin tokens, or any numeral.

isInitialTokenChar :: Char -> Bool

Tokens may begin with any alphabetic character or the characters in -./_:*+= ;

isQuoteableChar :: Char -> Bool

Only token characters and spaces don't need to be escaped when shown in the quoted syntax.

Transformations

fold :: (Sexpr t -> Sexpr t) -> Sexpr t -> Sexpr t

fold f s applies f to each sub-S-expression of s, from each leaf to the root. f need not preserve the shape of s, in contrast to the shape-preserving Traversable instance.

String printers

canonicalString :: Sexpr String -> String

basicString :: Sexpr String -> String

advancedString :: Sexpr String -> String

ShowS printers

canonical :: Sexpr String -> ShowS

Doc pretty printers

basic :: Sexpr String -> Doc

advanced :: Sexpr String -> Doc

Put binary printers

putCanonical :: Sexpr String -> Put

putCanonicalBS :: Sexpr ByteString -> Put

Parsers

readSexpr :: Read a => String -> Sexpr a

Read a Sexpr a using the Read instance for a. The Sexpr may be in any encoding: Canonical, Basic, or Advanced.

readSexprString :: String -> Sexpr String

Read a Sexpr String in any encoding: Canonical, Basic, or Advanced.

readCanonicalSexprString :: String -> Sexpr String

Read a Sexpr String in canonical encoding.

advancedSexpr :: ReadP (Sexpr String)

canonicalSexpr :: ReadP (Sexpr String)

For some applications it is wise to accept only very carefully specified input. This is useful when you know you are receiving exactly a Canonical S-Expression. It will read only a Canonical S-expression (and optional terminating NUL), but not the Basic or Advanced encodings.