A simple haskell string controls

Question

Theres a little problem I want to solve with Haskell: replace a function that changes all characters in a string for one specific parameter. The function has a de-signature:

subs :: String -> String -> String -> String
-- example:
-- subs 'x' "x^3 + x + sin(x)" "6.2" will generate
--          "6.2^3 + 6.2 + sin(6.2)"

Answer 1

You can use the Text.Regex package .

Your example might look something like this:

import Text.Regex(mkRegex, subRegex)

subs :: String -> String -> String -> String
subs wildcard input value = subRegex (mkRegex wildcard) input value

Answer 2

For such cases, you can use the text-format-simple library :

import Text.Format
format "{0}^3 + {0} + sin({0})" ["6.2"]

Answer 3

. http://bluebones.net/2007/01/replace-in-haskell/ , , .

Answer 4

(Text.Regex.Posix) search-replace /\Wx\W/ ( Perl). x 6.2 x + quux.

Haskell Regex Replace for more information (I think this should be imported into SO.

For an extra hard core, you can parse your expression as an AST and perform a replacement at that level.