| Maintainer | diagrams-discuss@googlegroups.com |
|---|---|
| Safe Haskell | Safe-Inferred |
Diagrams.Util
Description
Some miscellaneous utilities provided by the diagrams-lib package.
Utilities for users
Several functions exported by the diagrams library take a number
of arguments giving the user control to "tweak" various aspects
of their behavior. Rather than give such functions a long list
of arguments, and to make it possible for the user to selectively
override only certain arguments and use default values for
others, such sets of arguments are collected into a record with
named fields (see PolygonOpts in Diagrams.TwoD.Shapes for an
example). Such record types are made instances of the Default
class, which provides a single record structure (def)
collecting the "default" arguments to the function. with is
a synonym for def, which provides nice-looking syntax for
simulating optional, named arguments in Haskell. For example,
polygon with {sides = 7, edgeSkip = 2}
calls the polygon function with a single argument (note that
record update binds more tightly than function application!),
namely, with (the record of default arguments) where the
sides and edgeSkip fields have been updated.
applyAll :: [a -> a] -> a -> aSource
applyAll takes a list of functions and applies them all to a
value, in sequence from the last function in the list to the first.
For example, applyAll [f1, f2, f3] a == f1 . f2 . f3 $ a.
(#) :: a -> (a -> b) -> bSource
Postfix function application, for conveniently applying
attributes. Unlike ($), (#) has a high precedence (8), so d
# foo # bar can be combined with other things using operators
like (|||) or (<>) without needing parentheses.
iterateN :: Int -> (a -> a) -> a -> [a]Source
iterateN n f x returns the list of the first n iterates of
f starting at x, that is, the list [x, f x, f (f x), ...]
of length n. (Note that the last element of the list will be
f applied to x (n-1) times.)
The circle constant, the ratio of a circle's circumference to its
radius. Note that pi = tau/2.
For more information and a well-reasoned argument why we should all be using tau instead of pi, see The Tau Manifesto, http://tauday.com/.
To hear what it sounds like (and to easily memorize the first 30 digits or so), try http://youtu.be/3174T-3-59Q.