| Copyright | (c) 2011-2015 diagrams-lib team (see LICENSE) |
|---|---|
| License | BSD-style (see LICENSE) |
| Maintainer | diagrams-discuss@googlegroups.com |
| Safe Haskell | Safe-Inferred |
| Language | Haskell2010 |
Diagrams.Util
Description
Some miscellaneous utilities provided by the diagrams-lib package.
- with :: Default d => d
- applyAll :: [a -> a] -> a -> a
- (#) :: a -> (a -> b) -> b
- (##) :: AReview t b -> b -> t
- iterateN :: Int -> (a -> a) -> a -> [a]
- tau :: Floating a => a
- findHsFile :: FilePath -> IO (Maybe FilePath)
- findSandbox :: [FilePath] -> IO (Maybe FilePath)
- globalPackage :: IO FilePath
- foldB :: (a -> a -> a) -> a -> [a] -> a
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 -> a Source
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) -> b infixl 8 Source
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.
Finding files
findHsFile :: FilePath -> IO (Maybe FilePath) Source
Given some file (no extension or otherwise) try to find a haskell source file.
Finding sandboxes
findSandbox :: [FilePath] -> IO (Maybe FilePath) Source
Search for a sandbox in the following order:
- Test given FilePaths if they point directly to a database or contain a cabal config file (or any parent directory containing a config file).
- Same test for
DIAGRAMS_SANDBOXenvironment value - Environment values of
GHC_PACKAGE_PATH,HSENVandPACKAGE_DB_FOR_GHCthat point to a database. - Test for config file (cabal.sandbox.config) in the current directory and its parents.
globalPackage :: IO FilePath Source
Find ghc's global package database. Throws an error if it isn't found.