Data.Text.Format

Fast, efficient, flexible support for formatting text strings.

Types

data Format

A format string. This is intentionally incompatible with other string types, to make it difficult to construct a format string by concatenating string fragments (a very common way to accidentally make code vulnerable to malicious data).

This type is an instance of IsString, so the easiest way to construct a query is to enable the OverloadedStrings language extension and then simply write the query in double quotes.

 {-# LANGUAGE OverloadedStrings #-}

 import Data.Text.Format

 f :: Format
 f = "hello {}"

The underlying type is Text, so literal Haskell strings that contain Unicode characters will be correctly handled.

Instances

Eq Format

Ord Format

Show Format

Typeable Format

IsString Format

Monoid Format

newtype Only a

Use this newtype wrapper for your single parameter if you are formatting a string containing exactly one substitution site.

Constructors

Only

Fields

fromOnly :: a

Instances

Bounded a => Bounded (Only a)

Enum a => Enum (Only a)

Eq a => Eq (Only a)

Floating a => Floating (Only a)

Fractional a => Fractional (Only a)

Integral a => Integral (Only a)

Num a => Num (Only a)

Ord a => Ord (Only a)

Read a => Read (Only a)

Real a => Real (Only a)

RealFloat a => RealFloat (Only a)

RealFrac a => RealFrac (Only a)

Show a => Show (Only a)

Buildable a => Params (Only a)

Types for format control

newtype Shown a

Render a value using its Show instance.

Constructors

Shown

Fields

shown :: a

Instances

Bounded a => Bounded (Shown a)

Enum a => Enum (Shown a)

Eq a => Eq (Shown a)

Floating a => Floating (Shown a)

Fractional a => Fractional (Shown a)

Integral a => Integral (Shown a)

Num a => Num (Shown a)

Ord a => Ord (Shown a)

Read a => Read (Shown a)

Real a => Real (Shown a)

RealFloat a => RealFloat (Shown a)

RealFrac a => RealFrac (Shown a)

Show a => Show (Shown a)

Show a => Buildable (Shown a)

Rendering

format :: Params ps => Format -> ps -> Text

Render a format string and arguments to a Text.

print :: (MonadIO m, Params ps) => Format -> ps -> m ()

Render a format string and arguments, then print the result.

hprint :: (MonadIO m, Params ps) => Handle -> Format -> ps -> m ()

Render a format string and arguments, then print the result to the given file handle.

build :: Params ps => Format -> ps -> Builder

Render a format string and arguments to a Builder.

Format control

left :: Buildable a => Int -> Char -> a -> Builder

Pad the left hand side of a string until it reaches k characters wide, if necessary filling with character c.

right :: Buildable a => Int -> Char -> a -> Builder

Pad the right hand side of a string until it reaches k characters wide, if necessary filling with character c.

Integers

hex :: Integral a => a -> Builder

Render an integer using hexadecimal notation. (No leading 0x is added.)

Floating point numbers

expt

Arguments

:: Real a

=> Int

Number of digits of precision after the decimal.

-> a

-> Builder

Render a floating point number using scientific/engineering notation (e.g. 2.3e123), with the given number of decimal places.

fixed

Arguments

:: Real a

=> Int

Number of digits of precision after the decimal.

-> a

-> Builder

Render a floating point number using normal notation, with the given number of decimal places.

prec

Arguments

:: Real a

=> Int

Number of digits of precision.

-> a

-> Builder

Render a floating point number, with the given number of digits of precision. Uses decimal notation for values between 0.1 and 9,999,999, and scientific notation otherwise.

shortest :: Real a => a -> Builder

Render a floating point number using the smallest number of digits that correctly represent it.