Copyright	(c) 2018 Cedric Liegeois
License	BSD3
Maintainer	Cedric Liegeois <ofmooseandmen@yahoo.fr>
Stability	experimental
Portability	portable
Safe Haskell	Safe
Language	Haskell2010

Data.Geo.Jord.Eval

Contents

Orphan instances

Description

Types and functions for evaluating expressions in textual form.

Synopsis

data Value
- = Ang Angle
- | AngDec Double
- | Bool Bool
- | Double Double
- | Len Length
- | Gc GreatCircle
- | Geo GeoPos
- | Geos [GeoPos]
- | GeoDec (Double, Double)
- | GeosDec [(Double, Double)]
- | Vec NVector
- | Vecs [NVector]
data Vault
type Result = Either String Value
emptyVault :: Vault
eval :: String -> Vault -> Result
functions :: [String]
insert :: String -> Value -> Vault -> Vault
delete :: String -> Vault -> Vault
lookup :: String -> Vault -> Maybe Value

Documentation

data Value Source #

A value accepted and returned by eval.

Constructors

Ang Angle	`Angle`
AngDec Double	`Angle` in decimal degrees
Bool Bool	boolean
Double Double	double
Len Length	`Length`
Gc GreatCircle	`GreatCircle`
Geo GeoPos	`GeoPos`
Geos [GeoPos]	list of `GeoPos`
GeoDec (Double, Double)	latitude and longitude in decimal degrees
GeosDec [(Double, Double)]	list of latitude and longitude in decimal degrees
Vec NVector	`NVector`
Vecs [NVector]	list of `NVector`s

Instances

Eq Value Source #
Instance details Defined in Data.Geo.Jord.Eval Methods (==) :: Value -> Value -> Bool # (/=) :: Value -> Value -> Bool #
Show Value Source #
Instance details Defined in Data.Geo.Jord.Eval Methods showsPrec :: Int -> Value -> ShowS # show :: Value -> String # showList :: [Value] -> ShowS #

data Vault Source #

A location for Values to be shared by successive evalations.

type Result = Either String Value Source #

Either an error or a Value.

emptyVault :: Vault Source #

An empty Vault.

eval :: String -> Vault -> Result Source #

Evaluates s, an expression of the form "(f x y ..)".

>>> eval "finalBearing (destination (antipode 54°N,154°E) 54° 1000m) 54°N,154°E"
126°

f must be one of the supported functions and each parameter x, y, .. , is either another function call or a String parameter. Parameters are either resolved by name using the Resolve function r or if it returns Nothing, read to an Angle, a Length or a GeoPos.

If the evaluation is successful, returns the resulting Value (Right) otherwise a description of the error (Left).

    vault = emptyVault
    angle = eval "finalBearing 54N154E 54S154W" vault -- Right Ang
    length = eval "distance (antipode 54N154E) 54S154W" vault -- Right Len
    -- parameter resolution from vault
    a1 = eval "finalBearing 54N154E 54S154W" vault
    vault = insert "a1" vault
    a2 = eval "(finalBearing a1 54S154W)" vault

By default, all returned positions are Geo (GeoPos), to get back a Vec (NVector), the expression must be wrapped by toNVector.

    dest = eval "destination 54°N,154°E 54° 1000m" -- Right Geo
    dest = eval "toNVector (destination 54°N,154°E 54° 1000m)" -- Right Vec

Every function call must be wrapped between parentheses, however they can be ommitted for the top level call.

    angle = eval "finalBearing 54N154E 54S154W" -- Right Ang
    angle = eval "(finalBearing 54N154E 54S154W)" -- Right Ang
    length = eval "distance (antipode 54N154E) 54S154W" -- Right Len
    length = eval "distance antipode 54N154E 54S154W" -- Left String

functions :: [String] Source #

All supported functions:

insert :: String -> Value -> Vault -> Vault Source #

insert k v vault inserts value v for key k. Overwrites any previous value.

delete :: String -> Vault -> Vault Source #

delete k vault deletes key k from the vault.

lookup :: String -> Vault -> Maybe Value Source #

lookup k vault looks up the value of key k in the vault.

Orphan instances

MonadFail (Either String) Source #
Instance details Methods fail :: String -> Either String a #