diff --git a/Text/Numeral/Roman.hs b/Text/Numeral/Roman.hs --- a/Text/Numeral/Roman.hs +++ b/Text/Numeral/Roman.hs @@ -1,4 +1,5 @@ -{-# LANGUAGE FlexibleContexts +{-# LANGUAGE CPP + , FlexibleContexts , NoImplicitPrelude , OverloadedStrings , UnicodeSyntax @@ -7,11 +8,10 @@ {-| Parsing and pretty printing of Roman numerals. This module provides functions for parsing and pretty printing Roman -numerals. Because the notation of Roman numerals has varied through -the centuries this package allows for some customisation using a -configuration that is passed to the conversion functions. Exceptions -are dealt with by wrapping the results of conversions in the error -monad. +numerals. Because the notation of Roman numerals has varied through the +centuries this package allows for some customisation using a configuration that +is passed to the conversion functions. Exceptions are dealt with by wrapping the +results of conversions in the error monad. Example: @@ -21,8 +21,8 @@ @ @ - \> 'fromRoman' \"MDCCXXIX\" ∷ Either String Integer - Right 1729 + \> 'fromRoman' \"MDCCXXIX\" ∷ Maybe Integer + Just 1729 @ @ @@ -31,8 +31,8 @@ @ @ - \> 'fromRoman' \"Bla\" ∷ Either String Integer - Left \"Roman.convertFrom: can't parse\" + \> 'fromRoman' \"Bla\" ∷ Maybe Integer + Nothing @ -} @@ -62,47 +62,56 @@ ------------------------------------------------------------------------------- -- from base: +import Control.Monad ( return, mzero ) import Data.Bool ( Bool, otherwise ) -import Data.Char ( String ) import Data.Eq ( Eq ) import Data.Function ( ($), flip, on ) import Data.List ( sortBy, null, stripPrefix ) import Data.Maybe ( Maybe(Nothing, Just), maybe ) import Data.Monoid ( Monoid ) import Data.Ord ( Ord, compare ) -import Data.String ( IsString, fromString ) +import Data.String ( IsString ) import Data.Tuple ( snd ) -import Control.Monad ( (>>=), (>>), return, fail ) -import Prelude ( Num, (+), (-), fromInteger, error ) +import Prelude ( Num, (+), (-), error ) +#if __GLASGOW_HASKELL__ < 700 +import Control.Monad ( (>>=), (>>), fail ) +import Data.String ( fromString ) +import Prelude ( fromInteger ) +#endif + -- from base-unicode-symbols: import Data.Eq.Unicode ( (≡) ) -import Data.Function.Unicode ( (∘) ) -import Data.Ord.Unicode ( (≥), (≤) ) import Data.Monoid.Unicode ( (∅), (⊕) ) +import Data.Ord.Unicode ( (≥), (≤) ) -- from bytestring: -import qualified Data.ByteString as BS +import qualified Data.ByteString as BS ( ByteString + , isPrefixOf + , drop, length, null + ) +import qualified Data.ByteString.Lazy as BSL ( ByteString + , isPrefixOf + , drop, length, null + ) --- from monads-fd: -import Control.Monad.Error ( MonadError, throwError ) +-- from text: +import qualified Data.Text as T ( Text, null, stripPrefix ) +import qualified Data.Text.Lazy as TL ( Text, null, stripPrefix ) ------------------------------------------------------------------------------- -- Types ------------------------------------------------------------------------------- --- |A configuration with which the 'convertTo' and 'convertFrom' --- functions can be parameterized. +-- |A configuration with which the 'convertTo' and 'convertFrom' functions can +-- be parameterized. data NumeralConfig s n = NC { -- |Symbol to represent the value 0. ncZero ∷ s - -- |A table of symbols and their numerical values. The table - -- must be ordered in descending order of the value of the - -- symbols. If any symbol is the empty string then 'convertFrom' - -- will be ⊥. If any symbol in this table is associated - -- with the value 0 both the 'convertTo' and 'convertFrom' - -- function will be ⊥. + -- |A table of symbols and their numerical values. The table must be + -- ordered in descending order of the value of the symbols. If any symbol + -- is the empty string then 'convertFrom' will be ⊥. , ncTable ∷ [(s, n)] } @@ -117,16 +126,12 @@ , ncTable = sortBy (flip compare `on` snd) ((o, 1) : tab) } + ------------------------------------------------------------------------------- -- Pretty printing ------------------------------------------------------------------------------- --- |Converts a number to a Roman numeral according to the given --- configuration. Numbers which are out of bounds will cause --- exceptions to be thrown. An exception will also be raised if no --- representation is possible with the given configuration. If the --- value of any symbol in the configuration is equal to 0 or a symbol --- is the empty string this function is undefined. +-- |Converts a number to a Roman numeral according to the given configuration. convertTo ∷ Monoid s ⇒ Ord n ⇒ Num n ⇒ NumeralConfig s n → n → s convertTo nc n | n ≡ 0 = ncZero nc @@ -153,39 +158,51 @@ instance StripPrefix BS.ByteString where spNull = BS.null - spStripPrefix p s = let (h, t) = BS.breakSubstring p s - in if spNull h - then Just $ BS.drop (BS.length p) t - else Nothing + spStripPrefix p s = if p `BS.isPrefixOf` s + then Just $ BS.drop (BS.length p) s + else Nothing +instance StripPrefix BSL.ByteString where + spNull = BSL.null + spStripPrefix p s = if p `BSL.isPrefixOf` s + then Just $ BSL.drop (BSL.length p) s + else Nothing + +instance StripPrefix T.Text where + spNull = T.null + spStripPrefix = T.stripPrefix + +instance StripPrefix TL.Text where + spNull = TL.null + spStripPrefix = TL.stripPrefix + + -- |Parses a string as a Roman numeral according to the given --- configuration. An exception will be thrown if the input is not a --- valid numeral. -convertFrom ∷ (Monoid s, StripPrefix s, Eq s, Ord n, Num n, MonadError String m) - ⇒ NumeralConfig s n → s → m n +-- configuration. Result is 'Nothing' if the input is not a valid numeral. +convertFrom ∷ ( Monoid s, StripPrefix s, Eq s + , Ord n, Num n + ) + ⇒ NumeralConfig s n → s → Maybe n convertFrom nc s | ncZero nc ≡ s = return 0 | otherwise = do n ← (go 0 (ncTable nc) s) if s ≡ convertTo nc n then return n - else errMsg "invalid Roman numeral" + else mzero where go n _ x | spNull x = return n - go _ [] _ = errMsg "can't parse" + go _ [] _ = mzero go n tab@((sym, val) : ts) x = maybe (go n ts x) (go (n + val) tab) $ spStripPrefix sym x - errMsg = throwError ∘ ("Roman.convertFrom: " ⊕) - ------------------------------------------------------------------------------- -- Default Configurations ------------------------------------------------------------------------------- --- |Configuration for Roman numerals as they are commonly used --- today. The value 0 is represented by the empty string. It can be --- interpreted as not writing down a number. This configuration is --- practically limited to the range [1..3999]. Smaller numbers will --- result in empty string. Larger numbers will result in repeated use --- of the \'M\' symbol. +-- |Configuration for Roman numerals as they are commonly used today. The value +-- 0 is represented by the empty string. It can be interpreted as not writing +-- down a number. This configuration is practically limited to the range +-- [1..3999]. Smaller numbers will result in an empty string. Larger numbers +-- will result in repeated use of the \'M\' symbol. modernRoman ∷ (IsString s, Ord n, Num n) ⇒ NumeralConfig s n modernRoman = mkNumConfig "" @@ -204,12 +221,12 @@ , ("M", 1000) ] --- |Configuration for Roman numerals that do not use the rule that a --- lower rank symbol can be placed before a higher rank symbol to --- denote the difference between them. Thus a numeral like \"IV\" will --- not be accepted or generated by this configuration. This --- configuration is practically limited to the range [1..3999]. Larger --- numbers will result in repeated use of the \'M\' symbol. +-- |Configuration for Roman numerals that do not use the rule that a lower rank +-- symbol can be placed before a higher rank symbol to denote the difference +-- between them. Thus a numeral like \"IV\" will not be accepted or generated by +-- this configuration. This configuration is practically limited to the range +-- [1..3999]. Smaller numbers will result in an empty string. Larger numbers +-- will result in repeated use of the \'M\' symbol. simpleRoman ∷ (IsString s, Ord n, Num n) ⇒ NumeralConfig s n simpleRoman = mkNumConfig "" @@ -227,15 +244,12 @@ -- Utility ------------------------------------------------------------------------------- --- |Converts a number to a modern Roman numeral. See 'convertTo' for --- possible exceptions. +-- |Converts a number to a modern Roman numeral. toRoman ∷ (IsString s, Monoid s, Ord n, Num n) ⇒ n → s toRoman = convertTo modernRoman - --- |Parses a string as a modern Roman numeral. See 'convertFrom' for --- possible exceptions. +-- |Parses a string as a modern Roman numeral. fromRoman ∷ ( IsString s, Monoid s, StripPrefix s, Eq s - , Ord n, Num n, MonadError String m - ) ⇒ s → m n + , Ord n, Num n + ) ⇒ s → Maybe n fromRoman = convertFrom modernRoman diff --git a/roman-numerals.cabal b/roman-numerals.cabal --- a/roman-numerals.cabal +++ b/roman-numerals.cabal @@ -1,5 +1,5 @@ name: roman-numerals -version: 0.4.0.1 +version: 0.5.0 cabal-version: >= 1.6 build-type: Simple stability: stable @@ -26,7 +26,7 @@ build-depends: base >= 3.0.3.1 && < 4.4 , base-unicode-symbols >= 0.1.1 && < 0.3 , bytestring >= 0.9.1 && < 0.10 - , mtl >= 2.0.0.0 && < 2.1 + , text >= 0.11 && < 0.12 exposed-modules: Text.Numeral.Roman ghc-options: -Wall