Default arguments

Default arguments

since 0.3.7

It is possible to declare default arguments for functions using the @ operator.

 function := { "argument was: " + arg }@(arg:"default")

If this function is called without the arg argument, then the default value "default" is used instead. For example:

 function()                      == "argument was: default"
 function(arg: "something else") == "argument was: something else"

For determining whether the argument is set only explicit arguments count, not everything in scope, so

 arg := "something else"
 function()                      == "argument was: default"

Defaults are evaluated at the time the @ operator is evaluated, they will not be overriden later

 default  := "old default"
 function := { "argument was: " + arg }@(arg: default)
 default  := "new default"
 function()                      == "argument was: old default"

Rule functions

until 0.3.6

In earlier versions of MSE some functions were available in a special rule form. A call to for example replace_rule(match:"abc",replace:"xyz") is equivalent to replace@(match:"abc",replace:"xyz") . For backwards compatability these functions are still available, but they should not be used for new templates.

Programming in a rule style is still very useful. A rule is like a normal function with all parameters given, except for the input. These rules can then be combined using the + operator, for example:

 # First all "a"s are replaced, then all "b"s.
 remove_as_and_bs := replace@(match: "a", replace: "") +
                     replace@(match: "b", replace: "")
 
 text_with_as_and_bs := "bla bla bla"
 text_without_as_and_bs := remove_as_and_bs(text_with_as_and_bs)
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