Pattern Matching Example

Only contains a typechecker. Equipped with exhaustivity checking, meaning that it will check that all cases in a pattern match collectively cover everything that an input can be. For example, if constructors foo and bar are defined, it will trigger an error if there is only a case for foo; the input could be a bar, and we treat this as a compile-time error instead of a runtime error.

Also will give errors if certain patterns can never be hit. Using the same definitions as before, this can happen if there are two foo cases, in addition to a bar case.

Syntax

uname is a user-defined data type name
cname is a user-defined constructor name
x is a variable
i is an integer

type ::= `int` | uname
cdef ::= cname(type*)
tdef ::= `type` uname `=` cdef+
pattern ::= x | cname(pattern+)
case ::= `case` pattern `=>` exp
exp ::= i | x |
        | `let` x `=` exp `in` exp // variable introduction
        | cname(exp+) // constructor call
        | exp `match` { case+ } // pattern matching

Running

You will need sbt installed.

sbt
sbt> test