Pattern matching #40
Description
Purpose
Refer https://stackoverflow.com/questions/2502354/what-is-pattern-matching-in-functional-languages
Example
Shape = tags.case(circle.radius(Float)) case(square.side(Float))
(this Shape).area =
this.
case(circle.radius(0.0)):
(0.0)
case(square.side(0.0)):
(0.0)
case(circle.radius(r)):
(pi.*(r.square))
case(square.side(10.0)):
(100.0)
case(square):
(99999)Warning
There are many kinds of pattern matching:
- For tagged union
- For Integer
- For String
- For Record types
- On function arguments!
How to match function arguments?
Use record type matching as:
(this Boolean).or(that Boolean) =
record.left(this) right(that).
case(record.left(False) right(False)):
(False)
case(_):
(True)
Pattern matching with predicates
This can be achieve using lambdas. For example,
(this Shape).isBig =
case(circle.radius(.>(5.0)):
(Boolean.true)
case(square.side(.>(10.0)):
(Boolean.true)
case(rectangle.width(.>(5.0)) height(.>(5.0))):
(Boolean.true)
case(other):
(Boolean.false)