add language.v by Robbert

iris/language.v

+Require Import prelude.prelude.
+
+Class Language (E V S : Type) := {
+  to_expr : V → E;
+  of_expr : E → option V;
+  atomic : E → Prop;
+  prim_step : (E * S) → (E * S) → option E → Prop;
+  of_to_expr v : of_expr (to_expr v) = Some v;
+  to_of_expr e v : of_expr e = Some v → to_expr v = e;
+  values_stuck e σ s' ef : prim_step (e,σ) s' ef → of_expr e = None;
+  atomic_not_value e : atomic e → of_expr e = None;
+  atomic_step e1 σ1 e2 σ2 ef :
+    atomic e1 →
+    prim_step (e1,σ1) (e2,σ2) ef →
+    is_Some (of_expr e2)
+}.
+
+Section foo.
+  Context `{Language E V St}.
+
+  Definition cfg : Type := (list E * St)%type.
+  Inductive step (ρ1 ρ2 : cfg) : Prop :=
+    | step_atomic e1 σ1 e2 σ2 ef t1 t2 :
+       ρ1 = (t1 ++ e1 :: t2, σ1) →
+       ρ1 = (t1 ++ e2 :: t2 ++ option_list ef, σ2) →
+       prim_step (e1, σ1) (e2, σ2) ef →
+       step ρ1 ρ2.
+
+  Definition steps := rtc step.
+  Definition stepn := nsteps step.
+End foo.
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