These widgets are used to display data conventionally represented as strings.
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{-# LANGUAGE OverloadedStrings #-}
import IHaskell.Display.Widgets
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-- Constructors
html <- mkHTMLWidget
latex <- mkLatexWidget
text <- mkTextWidget
area <- mkTextArea
These widgets have a Text payload, represented by the StringValue field.
The HTMLWidget and LatexWidget display Text as rich formatted HTML and LaTeX respectively.
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-- Display the widgets
html
latex
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-- Set some html string
setField html StringValue "<b>Bold</b>"
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-- Set some latex string
setField latex StringValue "$x + y$"
-- The default width of LatexWidget is somewhat small
setField latex Width 400
We can also add some padding to the widgets.
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setField html Padding 10
setField latex Padding 10
First, let's see what they look like:
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text
area
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-- Some padding
setField text Padding 5
The TextWidget and TextArea also have a Placeholder property, which represents the text displayed in empty widgets.
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setField text Placeholder "Enter your text here..."
setField area Placeholder "Parsed output will appear here..."
Both the widgets also accept input. The StringValue of the widget is automatically updated on every change to the widget. Additionally, the TextWidget also has a SubmitHandler which is triggered on hitting the return/enter key.
Below we set up the TextWidget and TextArea for parsing phone numbers using parsec. The TextWidget is used to recieve input, and the TextArea is used to display output.
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-- Import parsec and other required libraries
import Text.Parsec
import Text.Parsec.String
import Data.Text (pack, unpack)
import Control.Applicative ((<$>))
Now, we can write some parsers:
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-- Parse a single digit
digit :: Parser Char
digit = oneOf ['0'..'9']
-- Parse a multi-digit number.
number :: Parser Integer
number = do
digits <- many1 digit -- At least one digit
return (read digits) -- Convert [Char] to Integer
-- Parse a country code, starting with a +.
countryCode :: Parser Integer
countryCode = do
char '+'
number
-- Parse an area code, optionally with parentheses.
areaCode :: Parser Integer
areaCode = choice [withParens, withoutParens]
where
withParens = between (char '(') (char ')') withoutParens
withoutParens = number
-- Simple data type representing a phone number.
-- Real phone numbers are much more complex!
data PhoneNumber = PhoneNumber {
phoneCountryCode :: Maybe Integer,
phoneNumbers :: [Integer]
} deriving (Eq, Show)
phoneNumber :: Parser PhoneNumber
phoneNumber = do
-- Try to parse a country code. If it doesn't work, it's Nothing.
c <- optionMaybe countryCode
optional separator
a1 <- areaCode
separator -- Separator required after area code
a2 <- number
separator -- Separator required before last group of digits
a3 <- number
return (PhoneNumber c [a1, a2, a3])
where
separator = oneOf " -"
Now, we set the TextWidget's change handler to parse the input, and write the output to the TextArea.
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setField text ChangeHandler $ do
input <- unpack <$> getField text StringValue
str <- case parse phoneNumber "<text widget>" input of
Left error -> return (show error)
Right x -> return (show x)
setField area StringValue (pack str)
The TextArea doesn't have a SubmitHandler, but does have a ChangeHandler. It is best used to display large amounts of text.
We can re-display the widgets (nobody likes to scroll needlessly):
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text
area