Text.ParserCombinators.Poly.Base

polyparse-1.11: A variety of alternative parser combinator libraries.

Safe Haskell | Safe
Language | Haskell98

Text.ParserCombinators.Poly.Base

Contents

- The PolyParse classes
- Combinators general to all parser types.
  - Simple combinators
  - Error-handling
  - Choices
  - Sequences

Synopsis

- class Commitment p where
  - commit :: p a -> p a
  - adjustErr :: p a -> (String -> String) -> p a
  - oneOf' :: [(String, p a)] -> p a
- class (Functor p, Monad p, Applicative p, Alternative p, Commitment p) => PolyParse p
- apply :: PolyParse p => p (a -> b) -> p a -> p b
- discard :: PolyParse p => p a -> p b -> p a
- failBad :: PolyParse p => String -> p a
- adjustErrBad :: PolyParse p => p a -> (String -> String) -> p a
- indent :: Int -> String -> String
- oneOf :: PolyParse p => [p a] -> p a
- exactly :: PolyParse p => Int -> p a -> p [a]
- upto :: PolyParse p => Int -> p a -> p [a]
- many1 :: PolyParse p => p a -> p [a]
- sepBy :: PolyParse p => p a -> p sep -> p [a]
- sepBy1 :: PolyParse p => p a -> p sep -> p [a]
- bracketSep :: PolyParse p => p bra -> p sep -> p ket -> p a -> p [a]
- bracket :: PolyParse p => p bra -> p ket -> p a -> p a
- manyFinally :: PolyParse p => p a -> p z -> p [a]
- manyFinally' :: (PolyParse p, Show a) => p a -> p z -> p [a]

# The PolyParse classes

class Commitment p where

The `Commitment` class is an abstraction over all the current concrete representations of monadic/applicative parser combinators in this package. The common feature is two-level error-handling. Some primitives must be implemented specific to each parser type (e.g. depending on whether the parser has a running state, or whether it is lazy). But given those primitives, large numbers of combinators do not depend any further on the internal structure of the particular parser.

Methods

commit :: p a -> p a

Commit is a way of raising the severity of any errors found within its argument. Used in the middle of a parser definition, it means that any operations prior to commitment fail softly, but after commitment, they fail hard.

adjustErr :: p a -> (String -> String) -> p a

`p `adjustErr` f` applies the transformation `f` to any error message generated in `p`, having no effect if `p` succeeds.

oneOf' :: [(String, p a)] -> p a

Parse the first alternative that succeeds, but if none succeed, report only the severe errors, and if none of those, then report all the soft errors.

Instances

Commitment Parser |
Commitment Parser |
Commitment Parser |
Commitment (Parser t) |
Commitment (Parser t) |
Commitment (Parser t) |
Commitment (Parser s) |
Commitment (Parser s t) |
Commitment (Parser s t) |

class (Functor p, Monad p, Applicative p, Alternative p, Commitment p) => PolyParse p

The `PolyParse` class is an abstraction gathering all of the common features that a two-level error-handling parser requires: the applicative parsing interface, the monadic interface, and commitment.

There are two additional basic combinators that we expect to be implemented afresh for every concrete type, but which (for technical reasons) cannot be class methods. They are `next` and `satisfy`.

Instances

PolyParse Parser |
PolyParse Parser |
PolyParse Parser |
PolyParse (Parser t) |
PolyParse (Parser t) |
PolyParse (Parser t) |
PolyParse (Parser s) |
PolyParse (Parser s t) |
PolyParse (Parser s t) |

# Combinators general to all parser types.

## Simple combinators

apply :: PolyParse p => p (a -> b) -> p a -> p b infixl 3

Apply a parsed function to a parsed value. Rather like ordinary function application lifted into parsers.

discard :: PolyParse p => p a -> p b -> p a infixl 3

`x `discard` y` parses both x and y, but discards the result of y. Rather like `const` lifted into parsers.

## Error-handling

failBad :: PolyParse p => String -> p a

When a simple fail is not strong enough, use failBad for emphasis. An emphasised (severe) error cannot be overridden by choice operators.

adjustErrBad :: PolyParse p => p a -> (String -> String) -> p a

`adjustErrBad` is just like `adjustErr` except it also raises the severity of the error.

indent :: Int -> String -> String

Helper for formatting error messages: indents all lines by a fixed amount.

## Choices

oneOf :: PolyParse p => [p a] -> p a

Parse the first alternative in the list that succeeds.

## Sequences

exactly :: PolyParse p => Int -> p a -> p [a]

'exactly n p' parses precisely n items, using the parser p, in sequence.

upto :: PolyParse p => Int -> p a -> p [a]

'upto n p' parses n or fewer items, using the parser p, in sequence.

many1 :: PolyParse p => p a -> p [a]

Parse a non-empty list of items.

sepBy :: PolyParse p => p a -> p sep -> p [a]

Parse a list of items separated by discarded junk.

sepBy1 :: PolyParse p => p a -> p sep -> p [a]

Parse a non-empty list of items separated by discarded junk.

bracketSep :: PolyParse p => p bra -> p sep -> p ket -> p a -> p [a]

Parse a list of items, discarding the start, end, and separator items.

bracket :: PolyParse p => p bra -> p ket -> p a -> p a

Parse a bracketed item, discarding the brackets. If everything matches except the closing bracket, the whole parse fails soft, which can give less-than-satisfying error messages. If you want better error messages, try calling with e.g. `bracket open (commit close) item`

manyFinally :: PolyParse p => p a -> p z -> p [a]

`manyFinally e t` parses a possibly-empty sequence of `e`'s, terminated by a `t`. The final `t` is discarded. Any parse failures could be due either to a badly-formed terminator or a badly-formed element, so it raises both possible errors.

manyFinally' :: (PolyParse p, Show a) => p a -> p z -> p [a]

`manyFinally'` is like `manyFinally`, except when the terminator parser overlaps with the element parser. In `manyFinally e t`, the parser `t` is tried only when parser `e` fails, whereas in `manyFinally' e t`, the parser `t` is always tried first, then parser `e` only if the terminator is not found. For instance, `manyFinally (accept "01") (accept "0")` on input `"0101010"` returns `["01","01","01"]`, whereas `manyFinally'` with the same arguments and input returns `[]`.