Portability | portable |
---|---|

Stability | stable |

Maintainer | Krasimir Angelov |

Safe Haskell | None |

This module is an Application Programming Interface to load and interpret grammars compiled in Portable Grammar Format (PGF). The PGF format is produced as a final output from the GF compiler. The API is meant to be used for embedding GF grammars in Haskell programs

- data PGF
- readPGF :: FilePath -> IO PGF
- data CId
- mkCId :: String -> CId
- wildCId :: CId
- showCId :: CId -> String
- readCId :: String -> Maybe CId
- type Language = CId
- showLanguage :: Language -> String
- readLanguage :: String -> Maybe Language
- languages :: PGF -> [Language]
- abstractName :: PGF -> Language
- languageCode :: PGF -> Language -> Maybe String
- data Type
- type Hypo = (BindType, CId, Type)
- showType :: [CId] -> Type -> String
- readType :: String -> Maybe Type
- mkType :: [Hypo] -> CId -> [Expr] -> Type
- mkHypo :: Type -> Hypo
- mkDepHypo :: CId -> Type -> Hypo
- mkImplHypo :: CId -> Type -> Hypo
- unType :: Type -> ([Hypo], CId, [Expr])
- categories :: PGF -> [CId]
- startCat :: PGF -> Type
- functions :: PGF -> [CId]
- functionsByCat :: PGF -> CId -> [CId]
- functionType :: PGF -> CId -> Maybe Type
- missingLins :: PGF -> Language -> [CId]
- type Tree = Expr
- data Expr
- showExpr :: [CId] -> Expr -> String
- readExpr :: String -> Maybe Expr
- mkAbs :: BindType -> CId -> Expr -> Expr
- unAbs :: Expr -> Maybe (BindType, CId, Expr)
- mkApp :: CId -> [Expr] -> Expr
- unApp :: Expr -> Maybe (CId, [Expr])
- mkStr :: String -> Expr
- unStr :: Expr -> Maybe String
- mkInt :: Int -> Expr
- unInt :: Expr -> Maybe Int
- mkDouble :: Double -> Expr
- unDouble :: Expr -> Maybe Double
- mkMeta :: Int -> Expr
- unMeta :: Expr -> Maybe Int
- linearize :: PGF -> Language -> Tree -> String
- linearizeAllLang :: PGF -> Tree -> [(Language, String)]
- linearizeAll :: PGF -> Tree -> [String]
- bracketedLinearize :: PGF -> Language -> Tree -> BracketedString
- tabularLinearizes :: PGF -> Language -> Expr -> [[(String, String)]]
- groupResults :: [[(Language, String)]] -> [(Language, [String])]
- showPrintName :: PGF -> Language -> CId -> String
- data BracketedString
- type FId = Int
- type LIndex = Int
- type Token = String
- showBracketedString :: BracketedString -> String
- flattenBracketedString :: BracketedString -> [String]
- parse :: PGF -> Language -> Type -> String -> [Tree]
- parseAllLang :: PGF -> Type -> String -> [(Language, [Tree])]
- parseAll :: PGF -> Type -> String -> [[Tree]]
- parse_ :: PGF -> Language -> Type -> Maybe Int -> String -> (ParseOutput, BracketedString)
- parseWithRecovery :: PGF -> Language -> Type -> [Type] -> Maybe Int -> String -> (ParseOutput, BracketedString)
- compute :: PGF -> Expr -> Expr
- paraphrase :: PGF -> Expr -> [Expr]
- checkType :: PGF -> Type -> Either TcError Type
- checkExpr :: PGF -> Expr -> Type -> Either TcError Expr
- inferExpr :: PGF -> Expr -> Either TcError (Expr, Type)
- data TcError
- = UnknownCat CId
- | UnknownFun CId
- | WrongCatArgs [CId] Type CId Int Int
- | TypeMismatch [CId] Expr Type Type
- | NotFunType [CId] Expr Type
- | CannotInferType [CId] Expr
- | UnresolvedMetaVars [CId] Expr [MetaId]
- | UnexpectedImplArg [CId] Expr
- | UnsolvableGoal [CId] MetaId Type

- ppTcError :: TcError -> Doc
- data ParseState
- initState :: PGF -> Language -> Type -> ParseState
- nextState :: ParseState -> ParseInput -> Either ErrorState ParseState
- getCompletions :: ParseState -> String -> Map Token ParseState
- recoveryStates :: [Type] -> ErrorState -> (ParseState, Map Token ParseState)
- data ParseInput = ParseInput {}
- simpleParseInput :: Token -> ParseInput
- mkParseInput :: PGF -> Language -> (forall a. b -> Map Token a -> Maybe a) -> [(CId, b -> Maybe (Tree, [Token]))] -> b -> ParseInput
- data ParseOutput
- = ParseFailed Int
- | TypeError [(FId, TcError)]
- | ParseOk [Tree]
- | ParseIncomplete

- getParseOutput :: ParseState -> Type -> Maybe Int -> (ParseOutput, BracketedString)
- generateAll :: PGF -> Type -> [Expr]
- generateAllDepth :: PGF -> Type -> Maybe Int -> [Expr]
- generateFrom :: PGF -> Expr -> [Expr]
- generateFromDepth :: PGF -> Expr -> Maybe Int -> [Expr]
- generateRandom :: RandomGen g => g -> PGF -> Type -> [Expr]
- generateRandomDepth :: RandomGen g => g -> PGF -> Type -> Maybe Int -> [Expr]
- generateRandomFrom :: RandomGen g => g -> PGF -> Expr -> [Expr]
- generateRandomFromDepth :: RandomGen g => g -> PGF -> Expr -> Maybe Int -> [Expr]
- type Lemma = CId
- type Analysis = String
- data Morpho
- lookupMorpho :: Morpho -> String -> [(Lemma, Analysis)]
- buildMorpho :: PGF -> Language -> Morpho
- fullFormLexicon :: Morpho -> [(String, [(Lemma, Analysis)])]
- morphoMissing :: Morpho -> [String] -> [String]
- mkTokenizer :: PGF -> Language -> String -> Maybe [String]
- graphvizAbstractTree :: PGF -> (Bool, Bool) -> Tree -> String
- graphvizParseTree :: PGF -> Language -> GraphvizOptions -> Tree -> String
- graphvizDependencyTree :: String -> Bool -> Maybe Labels -> Maybe String -> PGF -> CId -> Tree -> String
- graphvizBracketedString :: GraphvizOptions -> BracketedString -> String
- graphvizAlignment :: PGF -> [Language] -> Expr -> String
- gizaAlignment :: PGF -> (Language, Language) -> Expr -> (String, String, String)
- data GraphvizOptions = GraphvizOptions {}
- graphvizDefaults :: GraphvizOptions
- data Probabilities
- mkProbabilities :: PGF -> Map CId Double -> Probabilities
- defaultProbabilities :: PGF -> Probabilities
- showProbabilities :: Probabilities -> String
- readProbabilitiesFromFile :: FilePath -> PGF -> IO Probabilities
- browse :: PGF -> CId -> Maybe (String, [CId], [CId])

# PGF

readPGF :: FilePath -> IO PGFSource

Reads file in Portable Grammar Format and produces
`PGF`

structure. The file is usually produced with:

$ gf -make <grammar file name>

# Identifiers

An abstract data type that represents identifiers for functions and categories in PGF.

# Languages

This is just a `CId`

with the language name.
A language name is the identifier that you write in the
top concrete or abstract module in GF after the
concrete/abstract keyword. Example:

abstract Lang = ... concrete LangEng of Lang = ...

showLanguage :: Language -> StringSource

abstractName :: PGF -> LanguageSource

The abstract language name is the name of the top-level abstract module

languageCode :: PGF -> Language -> Maybe StringSource

Gets the RFC 4646 language tag
of the language which the given concrete syntax implements,
if this is listed in the source grammar.
Example language tags include `"en"`

for English,
and `"en-UK"`

for British English.

# Types

type Hypo = (BindType, CId, Type)Source

`Hypo`

represents a hypothesis in a type i.e. in the type A -> B, A is the hypothesis

showType :: [CId] -> Type -> StringSource

renders type as `String`

. The list
of identifiers is the list of all free variables
in the expression in order reverse to the order
of binding.

mkType :: [Hypo] -> CId -> [Expr] -> TypeSource

creates a type from list of hypothesises, category and
list of arguments for the category. The operation
`mkType [h_1,...,h_n] C [e_1,...,e_m]`

will create
`h_1 -> ... -> h_n -> C e_1 ... e_m`

mkImplHypo :: CId -> Type -> HypoSource

creates hypothesis for dependent type with implicit argument i.e. ({x} : A)

categories :: PGF -> [CId]Source

List of all categories defined in the given grammar. The categories are defined in the abstract syntax with the 'cat' keyword.

The start category is defined in the grammar with the 'startcat' flag. This is usually the sentence category but it is not necessary. Despite that there is a start category defined you can parse with any category. The start category definition is just for convenience.

# Functions

functionsByCat :: PGF -> CId -> [CId]Source

List of all functions defined for a given category

missingLins :: PGF -> Language -> [CId]Source

List of functions that lack linearizations in the given language.

# Expressions & Trees

## Tree

## Expr

An expression in the abstract syntax of the grammar. It could be both parameter of a dependent type or an abstract syntax tree for for some sentence.

showExpr :: [CId] -> Expr -> StringSource

renders expression as `String`

. The list
of identifiers is the list of all free variables
in the expression in order reverse to the order
of binding.

mkApp :: CId -> [Expr] -> ExprSource

Constructs an expression by applying a function to a list of expressions

# Operations

## Linearization

linearize :: PGF -> Language -> Tree -> StringSource

Linearizes given expression as string in the language

linearizeAllLang :: PGF -> Tree -> [(Language, String)]Source

Linearizes given expression as string in all languages available in the grammar.

linearizeAll :: PGF -> Tree -> [String]Source

The same as `linearizeAllLang`

but does not return
the language.

bracketedLinearize :: PGF -> Language -> Tree -> BracketedStringSource

Linearizes given expression as a bracketed string in the language

tabularLinearizes :: PGF -> Language -> Expr -> [[(String, String)]]Source

Creates a table from feature name to linearization. The outher list encodes the variations

data BracketedString Source

BracketedString represents a sentence that is linearized as usual but we also want to retain the ''brackets'' that mark the beginning and the end of each constituent.

Leaf Token | this is the leaf i.e. a single token |

Bracket CId !FId !LIndex CId [Expr] [BracketedString] | this is a bracket. The |

showBracketedString :: BracketedString -> StringSource

Renders the bracketed string as string where
the brackets are shown as `(S ...)`

where
`S`

is the category.

## Parsing

parse :: PGF -> Language -> Type -> String -> [Tree]Source

Tries to parse the given string in the specified language and to produce abstract syntax expression.

parseAllLang :: PGF -> Type -> String -> [(Language, [Tree])]Source

Tries to parse the given string with all available languages. The returned list contains pairs of language and list of abstract syntax expressions (this is a list, since grammars can be ambiguous). Only those languages for which at least one parsing is possible are listed.

parseAll :: PGF -> Type -> String -> [[Tree]]Source

The same as `parseAllLang`

but does not return
the language.

parse_ :: PGF -> Language -> Type -> Maybe Int -> String -> (ParseOutput, BracketedString)Source

The same as `parse`

but returns more detailed information

parseWithRecovery :: PGF -> Language -> Type -> [Type] -> Maybe Int -> String -> (ParseOutput, BracketedString)Source

This is an experimental function. Use it on your own risk

## Evaluation

paraphrase :: PGF -> Expr -> [Expr]Source

## Type Checking

The type checker in PGF does both type checking and renaming
i.e. it verifies that all identifiers are declared and it
distinguishes between global function or type indentifiers and
variable names. The type checker should always be applied on
expressions entered by the user i.e. those produced via functions
like `readType`

and `readExpr`

because otherwise unexpected results
could appear. All typechecking functions returns updated versions
of the input types or expressions because the typechecking could
also lead to metavariables instantiations.

checkType :: PGF -> Type -> Either TcError TypeSource

Check whether a given type is consistent with the abstract syntax of the grammar.

checkExpr :: PGF -> Expr -> Type -> Either TcError ExprSource

Checks an expression against a specified type.

inferExpr :: PGF -> Expr -> Either TcError (Expr, Type)Source

Tries to infer the type of a given expression. Note that
even if the expression is type correct it is not always
possible to infer its type in the GF type system.
In this case the function returns the `CannotInferType`

error.

If an error occurs in the typechecking phase
the type checker returns not a plain text error message
but a `TcError`

structure which describes the error.

UnknownCat CId | Unknown category name was found. |

UnknownFun CId | Unknown function name was found. |

WrongCatArgs [CId] Type CId Int Int | A category was applied to wrong number of arguments.
The first integer is the number of expected arguments and
the second the number of given arguments.
The |

TypeMismatch [CId] Expr Type Type | The expression is not of the expected type.
The first type is the expected type, while
the second is the inferred. The |

NotFunType [CId] Expr Type | Something that is not of function type was applied to an argument. |

CannotInferType [CId] Expr | It is not possible to infer the type of an expression. |

UnresolvedMetaVars [CId] Expr [MetaId] | Some metavariables have to be instantiated in order to complete the typechecking. |

UnexpectedImplArg [CId] Expr | Implicit argument was passed where the type doesn't allow it |

UnsolvableGoal [CId] MetaId Type | There is a goal that cannot be solved |

ppTcError :: TcError -> DocSource

Renders the type checking error to a document. See `PrettyPrint`

.

## Low level parsing API

data ParseState Source

An abstract data type whose values represent the current state in an incremental parser.

initState :: PGF -> Language -> Type -> ParseStateSource

Creates an initial parsing state for a given language and startup category.

nextState :: ParseState -> ParseInput -> Either ErrorState ParseStateSource

From the current state and the next token
`nextState`

computes a new state, where the token
is consumed and the current position is shifted by one.
If the new token cannot be accepted then an error state
is returned.

getCompletions :: ParseState -> String -> Map Token ParseStateSource

If the next token is not known but only its prefix (possible empty prefix)
then the `getCompletions`

function can be used to calculate the possible
next words and the consequent states. This is used for word completions in
the GF interpreter.

recoveryStates :: [Type] -> ErrorState -> (ParseState, Map Token ParseState)Source

data ParseInput Source

The input to the parser is a pair of predicates. The first one
`piToken`

selects a token from a list of suggestions from the grammar,
actually appears at the current position in the input string.
The second one `piLiteral`

recognizes whether a literal with forest id `FId`

could be matched at the current position.

simpleParseInput :: Token -> ParseInputSource

This function constructs the simplest possible parser input.
It checks the tokens for exact matching and recognizes only `String`

, `Int`

and `Float`

literals.
The `Int`

and `Float`

literals match only if the token passed is some number.
The `String`

literal always match but the length of the literal could be only one token.

mkParseInput :: PGF -> Language -> (forall a. b -> Map Token a -> Maybe a) -> [(CId, b -> Maybe (Tree, [Token]))] -> b -> ParseInputSource

data ParseOutput Source

This data type encodes the different outcomes which you could get from the parser.

ParseFailed Int | The integer is the position in number of tokens where the parser failed. |

TypeError [(FId, TcError)] | The parsing was successful but none of the trees is type correct.
The forest id ( |

ParseOk [Tree] | If the parsing and the type checking are successful we get a list of abstract syntax trees. The list should be non-empty. |

ParseIncomplete | The sentence is not complete. Only partial output is produced |

getParseOutput :: ParseState -> Type -> Maybe Int -> (ParseOutput, BracketedString)Source

This function extracts the list of all completed parse trees that spans the whole input consumed so far. The trees are also limited by the category specified, which is usually the same as the startup category.

## Generation

The PGF interpreter allows automatic generation of abstract syntax expressions of a given type. Since the type system of GF allows dependent types, the generation is in general undecidable. In fact, the set of all type signatures in the grammar is equivalent to a Turing-complete language (Prolog).

There are several generation methods which mainly differ in:

- whether the expressions are sequentially or randomly generated?
- are they generated from a template? The template is an expression containing meta variables which the generator will fill in.
- is there a limit of the depth of the expression? The depth can be used to limit the search space, which in some cases is the only way to make the search decidable.

generateAll :: PGF -> Type -> [Expr]Source

Generates an exhaustive possibly infinite list of abstract syntax expressions.

generateAllDepth :: PGF -> Type -> Maybe Int -> [Expr]Source

A variant of `generateAll`

which also takes as argument
the upper limit of the depth of the generated expression.

generateFrom :: PGF -> Expr -> [Expr]Source

Generates a list of abstract syntax expressions
in a way similar to `generateAll`

but instead of
generating all instances of a given type, this
function uses a template.

generateFromDepth :: PGF -> Expr -> Maybe Int -> [Expr]Source

A variant of `generateFrom`

which also takes as argument
the upper limit of the depth of the generated subexpressions.

generateRandom :: RandomGen g => g -> PGF -> Type -> [Expr]Source

Generates an infinite list of random abstract syntax expressions. This is usefull for tree bank generation which after that can be used for grammar testing.

generateRandomDepth :: RandomGen g => g -> PGF -> Type -> Maybe Int -> [Expr]Source

A variant of `generateRandom`

which also takes as argument
the upper limit of the depth of the generated expression.

generateRandomFrom :: RandomGen g => g -> PGF -> Expr -> [Expr]Source

Random generation based on template

generateRandomFromDepth :: RandomGen g => g -> PGF -> Expr -> Maybe Int -> [Expr]Source

Random generation based on template with a limitation in the depth.

## Morphological Analysis

buildMorpho :: PGF -> Language -> MorphoSource

morphoMissing :: Morpho -> [String] -> [String]Source

## Tokenizing

mkTokenizer :: PGF -> Language -> String -> Maybe [String]Source

This is the construction function. Given a PGF and a Language, it extract the lexicon for this language and build a tokenization fst from it.

## Visualizations

graphvizAbstractTree :: PGF -> (Bool, Bool) -> Tree -> StringSource

Renders abstract syntax tree in Graphviz format

graphvizParseTree :: PGF -> Language -> GraphvizOptions -> Tree -> StringSource

graphvizDependencyTree :: String -> Bool -> Maybe Labels -> Maybe String -> PGF -> CId -> Tree -> StringSource

data GraphvizOptions Source

# Probabilities

data Probabilities Source

An abstract data structure which represents the probabilities for the different functions in a grammar.

mkProbabilities :: PGF -> Map CId Double -> ProbabilitiesSource

Builds probability tables. The second argument is a map which contains the know probabilities. If some function is not in the map then it gets assigned some probability based on the even distribution of the unallocated probability mass for the result category.

defaultProbabilities :: PGF -> ProbabilitiesSource

Returns the default even distibution.

showProbabilities :: Probabilities -> StringSource

Renders the probability structure as string

readProbabilitiesFromFile :: FilePath -> PGF -> IO ProbabilitiesSource

Reads the probabilities from a file. This should be a text file where on every line there is a function name followed by a real number. The number represents the probability mass allocated for that function. The function name and the probability should be separated by a whitespace.