Data.Geo.Jord.Eval

Types and functions for evaluating expressions in textual form.

Documentation

data Value

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

Ll LatLong

LatLong

Lls [LatLong]

list of LatLong

LlDec (Double, Double)

latitude and longitude in decimal degrees

LlsDec [(Double, Double)]

list of latitude and longitude in decimal degrees

Vec NVector

NVector

Vecs [NVector]

list of NVectors

Instances

Eq Value

Defined in Data.Geo.Jord.Eval

Methods

(==) :: Value -> Value -> Bool

(/=) :: Value -> Value -> Bool

Show Value

Defined in Data.Geo.Jord.Eval

Methods

showsPrec :: Int -> Value -> ShowS

show :: Value -> String

showList :: [Value] -> ShowS

data Vault

 A location for Values to be shared by successive evalations.

type Result = Either String Value

Either an error or a Value.

emptyVault :: Vault

An empty Vault.

eval :: String -> Vault -> Result

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 LatLong.

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

All returned positions are LatLong by default, to get back a NVector the expression must be wrapped by toNVector.

    dest = eval "destination 54°N,154°E 54° 1000m" -- Right Ll
    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]

All supported functions:

• antipode
• crossTrackDistance
• decimalDegrees
• destination
• distance
• finalBearing
• greatCircle
• initialBearing
• interpolate
• intersections
• isInside
• mean
• latLong
• latLongDecimal
• readLatLong
• toDecimalDegrees
• toKilometres
• toMetres
• toNauticalMiles
• toNVector

insert :: String -> Value -> Vault -> Vault

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

delete :: String -> Vault -> Vault

delete k vault deletes key k from the vault.

lookup :: String -> Vault -> Maybe Value

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

Orphan instances

MonadFail (Either String)

Methods

fail :: String -> Either String a