feat(library/init/lean/metavarcontext): add basic functions

library/init/lean/metavarcontext.lean

@@ -31,5 +31,41 @@ structure MetavarContext :=
 
 namespace MetavarContext
 
+/- Low level API for creating metavariable declarations.
+   It is used to implement actions in the monads `Elab` and `Tactic`.
+   It should not be used directly since the argument `(mvarId : Name)` is assumed to be "unique". -/
+def mkDecl (m : MetavarContext) (mvarId : Name) (userName : Name) (lctx : LocalContext) (type : Expr) : MetavarContext :=
+{ decls := m.decls.insert mvarId { userName := userName, lctx := lctx, type := type }, .. m }
+
+def findDecl (m : MetavarContext) (mvarId : Name) : Option MetavarDecl :=
+m.decls.find mvarId
+
+def assignLevel (m : MetavarContext) (mvarId : Name) (val : Level) : MetavarContext :=
+{ lAssignment := m.lAssignment.insert mvarId val, .. m }
+
+def assignExpr (m : MetavarContext) (mvarId : Name) (val : Expr) : MetavarContext :=
+{ eAssignment := m.eAssignment.insert mvarId val, .. m }
+
+def assignDelayed (m : MetavarContext) (mvarId : Name) (lctx : LocalContext) (fvars : List Expr) (val : Expr) : MetavarContext :=
+{ dAssignment := m.dAssignment.insert mvarId { lctx := lctx, fvars := fvars, val := val }, .. m }
+
+def getLevelAssignment (m : MetavarContext) (mvarId : Name) : Option Level :=
+m.lAssignment.find mvarId
+
+def getExprAssignment (m : MetavarContext) (mvarId : Name) : Option Expr :=
+m.eAssignment.find mvarId
+
+def getDelayedAssignment (m : MetavarContext) (mvarId : Name) : Option DelayedMetavarAssignment :=
+m.dAssignment.find mvarId
+
+def isLevelAssigned (m : MetavarContext) (mvarId : Name) : Bool :=
+m.lAssignment.contains mvarId
+
+def isExprAssigned (m : MetavarContext) (mvarId : Name) : Bool :=
+m.eAssignment.contains mvarId
+
+def istDelayedAssigned (m : MetavarContext) (mvarId : Name) : Bool :=
+m.dAssignment.contains mvarId
+
 end MetavarContext
 end Lean