Control.Category.Printf

Documentation

module Control.Category

Basics

type Format m = Cokleisli ((->) m)

Handy type synonym for the things we're working with. You should regard a value of type Format m a b as something which explains how to write some element of the monoid m (a "string" for our purposes), and which will change the type of printf from a to b. For instance, something which adds a responsibility to provide an additional argument of type t might have type Format m a (t -> a), while a formatter which somehow absolves you of that responsibility would have type Format m (t -> a) a.

printfWith :: (m -> r) -> Format m r b -> b

We can apply this to something like putStrLn to get a function for formatted printing. Typically you'll have r = IO (), but that needn't be the case.

sprintf :: Format m m b -> b

If you just want to build a string / element of your monoid, we have sprintf = printfWith id

c :: Monoid m => m -> Format m a a

Formatter for a constant string.

i :: Format m a (m -> a)

Inclusion of a string as an argument.

spliceWith :: Monoid m => (t -> m) -> Format m a (t -> a)

Given a way to turn a value of type t into a string, this builds a formatter which demands an additional argument of type t and splices it in.

s :: (Monoid s, IsString s, Show t) => Format s a (t -> a)

Splice in anything showable.

generalizeString :: (IsString s, Monoid s) => Format String a b -> Format s a b

Generalizes the string type that a formatter uses by applying fromString internally.

Numeric formatting

intAtBase :: (Real t, Integral t, Show t, Monoid s, IsString s) => t -> (Int -> Char) -> Format s a (t -> a)

Show an integral value using the given base, and using the provided function to determine how to display individual digits.

hex :: (Integral t, Show t, Monoid s, IsString s) => Format s a (t -> a)

Show an integral value in hexadecimal.

oct :: (Integral t, Show t, Monoid s, IsString s) => Format s a (t -> a)

Show an integral value in octal.

eFloat :: (RealFloat t, Monoid s, IsString s) => Maybe Int -> Format s a (t -> a)

Show a floating point value in exponential format. (e.g. 2.45e2, -1.5e-3) If digs is Nothing, the value is shown to full precision, if it is Just d then at most d digits after the decimal point are shown.

fFloat :: (RealFloat t, Monoid s, IsString s) => Maybe Int -> Format s a (t -> a)

Show a floating point value in standard decimal format. (e.g. 245000, -0.0015) If digs is Nothing, the value is shown to full precision, if it is Just d then at most d digits after the decimal point are shown.

gFloat :: (RealFloat t, Monoid s, IsString s) => Maybe Int -> Format s a (t -> a)

Show a floating point value using standard decimal notation for arguments whose absolute value lies between 0.1 and 9,999,999, and scientific notation otherwise. If digs is Nothing, the value is shown to full precision, if it is Just d then at most d digits after the decimal point are shown.

Argument stack manipulation

push :: Monoid m => t -> Format m (t -> a) a

We can use arr from the Arrow instance for Cokleisli w to produce formatters that manipulate the stack without printing. That is, we have

arr :: (Monoid m) => (s -> s') -> Format m s s'

Push an argument onto the stack to be consumed by subsequent formatters.

dup :: Monoid m => Format m (t -> t -> a) (t -> a)

Duplicate an argument on the stack, making it available twice.

swap :: Monoid m => Format m (t -> t' -> a) (t' -> t -> a)

Swap the next two arguments on the stack.

skip :: Monoid m => Format m (t -> a) (t' -> t -> a)

Skip the next argument on the stack.

apply :: Monoid m => (u -> v) -> Format m (v -> a) (u -> a)

Apply a function to the argument on the top of the stack.

apply2 :: Monoid m => (u -> v -> w) -> Format m (w -> a) (u -> v -> a)

Apply a binary function to the top two arguments on the stack.

Orphan instances

((~) * a b, IsString s, Monoid s) => IsString (Cokleisli ((->) s) a b)

Methods

fromString :: String -> Cokleisli ((->) s) a b