Control.Egison.QQ

Quasiquotation for rewriting a match clause.

Documentation

mc :: QuasiQuoter

A quasiquoter for rewriting a match clause. This quasiquoter is useful for generating a MatchClause in user-friendly syntax.

Wildcards

A match clause that contains a wildcard

[mc| _ => "Matched" |]

is rewritten to

MatchClause Wildcard
            (\HNil -> "Matched")

Pattern variables

A match clause that contains a pattern variable

[mc| $x => x |]

is rewritten to

MatchClause (PatVar "x")
            (\HCons x HNil -> x)

Value patterns

A match clause that contains a value pattern

[mc| cons $x (cons $y (cons #(x + 1) (cons $z nil))) => (x, y, z) |]

is rewritten to

MatchClause (cons (PatVar "x") (cons (PatVar "y") (cons (ValuePat (\HCons x (HCons (y HNil)) -> x + 1)) (cons (PatVar "z") nil))))
            (\HCons x (HCons (y (HCons z HNil))) -> (x, y, z))

And-patterns

A match clause that contains an and-pattern

[mc| (cons _ _) & $x => x |]

is rewritten to

MatchClause (AndPat (cons Wildcard Wildcard) (PatVar "x"))
            (\HCons x HNil -> x)

Or-patterns

A match clause that contains an or-pattern

[mc| nil | (cons _ _) => "Matched" |]

is rewritten to

MatchClause (OrPat nil (cons Wildcard Wildcard))
            (\HNil -> "Matched")

Collection patterns

A collection pattern

[p1, p2, ..., pn]

is desugared into

p1 : p2 : ... : pn : nil

Cons patterns

A pattern with special collection pattern operator :

p1 : p2

is parsed as

p1 `cons` p2

Join patterns

A pattern with special collection pattern operator ++

p1 ++ p2

is parsed as

p1 `join` p2