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

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

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

Exported compatibility functor, abstracted over constructor equality

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.

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

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 '_'

ppat_of_type builds an untyped pattern from its expected type, for explosion of wildcard patterns in Typecore.type_pat.

There are four interesting cases:

• the type is empty (PT_empty)
• no further explosion is necessary (PT_any)
• a single pattern is generated, from a record or tuple type or a single-variant type (PE_single)
• an or-pattern is generated, in the case that all branches are GADT constructors (PE_gadt_cases).

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.

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.