Type: Package
Title: Optional Types and Pattern Matching
Version: 2.0.1
Date: 2022-04-27
Author: Antoine Champion
Maintainer: Antoine Champion <antoine.champion@outlook.com>
Description: Introduces optional types with some() and none, as well as match_with() from functional languages.
License: BSL
Imports: methods, magrittr
RoxygenNote: 6.0.1
Suggests: knitr, rmarkdown
VignetteBuilder: knitr
NeedsCompilation: no
Packaged: 2022-04-27 17:12:32 UTC; antoi
Repository: CRAN
Date/Publication: 2022-04-27 17:40:03 UTC

Fallthrough function

Description

Permit a pattern matching to continue even if its argument is executed.

Usage

fallthrough(fun)

Arguments

fun

A result function used in make_opt()

Details

fallthrough(fun) can be applied to a result function fun inside a match_with() pattern. If there is a match, this will make the pattern matching continue through the other conditions at the end of the result function fun. match_with(variable, pattern, fallthrough(result-function), ...

Examples

library(magrittr)

a <- 4
match_with(a,
  . %>% if (. %% 2 == 0)., 
  fallthrough( function() "This number is even" ),
  . %>% if ( sqrt(.) == round(sqrt(.)) ).,  
  function() "This number is a perfect square"
)
## [1] "This number is even"   "This number is a perfect square"

Make optional

Description

Make an existing function accepting and returning optionals.

Usage

make_opt(fun, stop_if_none = FALSE, fun_if_none = NULL)

Arguments

fun

The function to make optional, might be any function.

stop_if_none

If true, f_opt() will stop and return none if one of the arguments provided is none. Else, none will be sent as NULL to the function. *Default: FALSE*

fun_if_none

If not null, will be executed if an argument is none. *Default: NULL*

Details

  1. Every optional argument passed to f_opt() will be converted to its original type before being sent to f(). If one or more of them is none, several behaviors are available (see argument list).

  2. If f() returns null, or if an error is thrown during its execution, then f_opt() returns none. Else it will return option(f(...)).

Value

The optional function. To be used with the same parameters than fun().

See Also

option(), none(), match_with()

Examples

c_opt <- make_opt(c)
c_opt(option(2), none, option(5))
## [1] 2 5
c_opt()
## [1] "None"

Match With

Description

Function to check a variable using pattern matching.

Usage

match_with(x, ...)

Arguments

x

The variable to pattern-match

...

Pairs of one pattern (value or list or magrittr sequence) and one result function

Details

match_with(variable, pattern, result-function, ... If variable matches a pattern, result-function is called. For comparing optional types, it is a better habit to use match_with than a conditional statement.

  1. Each pattern can be either:

    • an object or a primitive type (direct comparison with variable),

    • a list (match if variable is in the list),

    • a magrittr functional sequence that matches if it returns variable . The dot . denotes the variable to be matched.

  2. If result-function takes no arguments, it will be called as is. Else, the only argument that will be sent is variable. You can also use the fallthrough function fallthrough() to permit the matching to continue even if the current pattern is matched.

See Also

option(), none

Examples

library(magrittr)

a <- 5
match_with(a,
  . %>% option(.),     paste,
  none, function()   "Error!"
)
## [1] 5

match_with(a,
  1,                   function()  "Matched exact value",
  list(2, 3, 4),       function(x) paste("Matched in list:", x),
  . %>% if (. > 4) .,  function(x) paste("Matched in condition:", x)
)
## [1] "Matched in condition: 5"

None

Description

Indicates an invalid variable. Might be returned by an optional function (see ?make_opt())

Usage

none

Format

An object of class optional of length 1.

See Also

option(), opt_unwrap()

Examples

a <- none
a
## [1] None

Option Unwrap

Description

Cast an optional object to its base type.

Usage

opt_unwrap(opt)

Arguments

opt

The optional variable to cast back

Details

Since an optional can be used the same way as its base type, there is no known scenario where this function might be useful.

Value

The object wrapped in opt. NULL if opt is none.

See Also

make_opt(), match_with()

Examples

a <- option(5)
class(a)
## [1] "optional"
a <- opt_unwrap(a)

class(a)
## [1] "numeric"

option

Description

Make a variable optional.

option is an object wrapper which indicates whether the object is valid or not.

Usage

option(arg)

Arguments

arg

The variable to make optional

Details

Note that option(option(i)) == option(i) and option(none) == FALSE

Operators and print will have the same behavior with an optional than with its base type.

Value

arg as optional

See Also

none, opt_unwrap(), make_opt()

Examples

a <- option(5)
class(a)
## [1] "optional"

a == 5
## [1] TRUE

a
## [1] 5

some

Description

Check if a optional object equals none

Usage

some(arg)

Arguments

arg

The variable to check existence

Value

TRUE if arg is an optional variable and if it is not none, else returns FALSE

See Also

option(), none a <- option(1) some(a) ## [1] TRUE b <- none some(b) ## [1] FALSE