purescript-verbal-expressions

A free monad implementation of Verbal Expressions for PureScript.

Examples

Basic testing

We can use do-notation to construct verbal expressions:

number :: VerEx
number = do
  startOfLine
  possibly (anyOf "+-")
  some digit
  possibly do
    find "."
    some digit
  endOfLine

> test number "42"
true

> test number "+3.14"
true

> test number "3."
false

The monadic interface allows us to bind the indices of capture groups to named expressions:

pattern :: VerEx
pattern = do
  firstWord <- capture word
  whitespace
  word
  whitespace
  findAgain firstWord

This pattern matches "foo bar foo" but not "foo bar baz".

Matching

Here, we use the result of the monadic action to return an array of capture groups. Note that optional capturing groups are possible:

number = do
  startOfLine
  intPart <- capture (some digit)
  floatPart <- possibly do
    find "."
    capture (some digit)
  endOfLine
  pure [intPart, floatPart]

> match number "3.14"
Just [Just "3", Just "14"]

> match number "42"
Just [Just "42", Nothing]

> match number "."
Nothing

Replacing

If, instead, we return a string from the monadic action, we can use it as a replacement string (with 'named' capture groups):

swapWords :: String -> String
swapWords = replace do
  first  <- capture word
  blank  <- capture (some whitespace)
  second <- capture word

  replaceWith (insert second <> insert blank <> insert first)

> swapWords "Foo   Bar"
"Bar   Foo"

Note that replaceWith is just an alias for pure.

For more examples, see the tests.

Installation

bower install purescript-verbal-expressions