app function
Implementation
App app(
FuncDecl decl, [
Expr? x1,
Expr? x2,
Expr? x3,
Expr? x4,
Expr? x5,
Expr? x6,
Expr? x7,
Expr? x8,
Expr? x9,
]) =>
App(decl, [
if (x1 != null) x1,
if (x2 != null) x2,
if (x3 != null) x3,
if (x4 != null) x4,
if (x5 != null) x5,
if (x6 != null) x6,
if (x7 != null) x7,
if (x8 != null) x8,
if (x9 != null) x9,
]).declare();