# Library Coq.micromega.DeclConstant

Declaring 'allowed' terms using type classes.
Motivation: reification needs to know which terms are allowed.
For 'lia', the constant are only the integers built from Z0, Zpos, Zneg, xH, xO, xI.
However, if the term is ground it may be convertible to an integer.
Thus we could allow i.e. sqrt z for some integer z.
Proposal: for each type, the user declares using type-classes the set of allowed ground terms.

Declarative definition of constants.
These are ground terms (without variables) of interest.
e.g. nat is built from O and S
NB: this does not need to be restricted to constructors.
Ground terms (see GT below) are built inductively from declared constants.

Class DeclaredConstant {T : Type} (F : T).

Class GT {T : Type} (F : T).

Instance GT_O {T : Type} (F : T) {DC : DeclaredConstant F} : GT F.

Defined.

Instance GT_APP1 {T1 T2 : Type} (F : T1 -> T2) (A : T1) :

DeclaredConstant F ->

GT A -> GT (F A).

Defined.

Instance GT_APP2 {T1 T2 T3: Type} (F : T1 -> T2 -> T3)

{A1 : T1} {A2 : T2} {DC:DeclaredConstant F} :

GT A1 -> GT A2 -> GT (F A1 A2).

Defined.

Require Import QArith_base.

Instance DO : DeclaredConstant O := {}.

Instance DS : DeclaredConstant S := {}.

Instance DxH: DeclaredConstant xH := {}.

Instance DxI: DeclaredConstant xI := {}.

Instance DxO: DeclaredConstant xO := {}.

Instance DZO: DeclaredConstant Z0 := {}.

Instance DZpos: DeclaredConstant Zpos := {}.

Instance DZneg: DeclaredConstant Zneg := {}.

Instance DZpow_pos : DeclaredConstant Z.pow_pos := {}.

Instance DZpow : DeclaredConstant Z.pow := {}.

Instance DQ : DeclaredConstant Qmake := {}.