Module Melange_compiler_libs.Parmatch

Detection of partial matches and unused match cases.

type 'pattern parmatch_case = {
  1. pattern : 'pattern;
  2. has_guard : bool;
  3. needs_refute : bool;
    (*

    true if the program text claims the case is unreachable, a la function _ -> .

    *)
}

Most checks in this file need not access all information about a case, and just need a few pieces of information. parmatch_case is those few pieces of information.

type 'category typed_case := 'category Typedtree.general_pattern parmatch_case
val typed_case : 'category Typedtree.case -> 'category typed_case
val untyped_case : Parsetree.case -> Parsetree.pattern parmatch_case
val const_compare : Asttypes.constant -> Asttypes.constant -> int

const_compare c1 c2 compares the actual values represented by c1 and c2, while simply using Stdlib.compare would compare the representations.

cf. MPR#5758

val le_pat : Typedtree.pattern -> Typedtree.pattern -> bool

le_pat p q means: forall V, V matches q implies V matches p

val le_pats : Typedtree.pattern list -> Typedtree.pattern list -> bool

le_pats (p1 .. pm) (q1 .. qn) means: forall i <= m, le_pat pi qi

module Compat (_ : sig ... end) : sig ... end

Exported compatibility functor, abstracted over constructor equality

exception Empty

lub p q is a pattern that matches all values matched by p and q. May raise Empty, when p and q are not compatible.

val lubs : Typedtree.pattern list -> Typedtree.pattern list -> Typedtree.pattern list

lubs [p1; ...; pn] [q1; ...; qk], where n < k, is [lub p1 q1; ...; lub pk qk].

val get_mins : ('a -> 'a -> bool) -> 'a list -> 'a list

Those two functions recombine one pattern and its arguments: For instance: (_,_)::p1::p2::rem -> (p1, p2)::rem The second one will replace mutable arguments by '_'

val set_args_erase_mutable : Typedtree.pattern -> Typedtree.pattern list -> Typedtree.pattern list
val pats_of_type : Env.t -> Types.type_expr -> Typedtree.pattern list

pats_of_type builds a list of patterns from a given expected type, for explosion of wildcard patterns in Typecore.type_pat.

There are four interesting cases:

  • the type is empty ()
  • no further explosion is necessary (Pat_any)
  • a single pattern is generated, from a record or tuple type or a single-variant type (tp)
  • a list of patterns, in the case that all branches are GADT constructors (tp1; ..; tpn).
val pressure_variants : Env.t -> Typedtree.pattern list -> unit
val pressure_variants_in_computation_pattern : Env.t -> Typedtree.computation Typedtree.general_pattern list -> unit

check_partial pred loc caselist and check_unused refute pred caselist are called with a function pred which will be given counter-example candidates: they may be partially ill-typed, and have to be type-checked to extract a valid counter-example. pred returns a valid counter-example or None. refute indicates that check_unused was called on a refutation clause.

val check_unused : (bool -> Typedtree.pattern -> Typedtree.pattern option) -> Typedtree.value typed_case list -> unit
val irrefutable : Typedtree.pattern -> bool
val inactive : partial:Typedtree.partial -> Typedtree.pattern -> bool

An inactive pattern is a pattern, matching against which can be duplicated, erased or delayed without change in observable behavior of the program. Patterns containing (lazy _) subpatterns or reads of mutable fields are active.

val check_ambiguous_bindings : Typedtree.value Typedtree.case list -> unit
val some_private_tag : Asttypes.label