Refinement Types for TypeScript

1.1 Object Constraint System Our system leverages the idea introduced in the formall core of X10 [3] to extend a base constraint system C with a larger constraint system O (C), built on top of C. The original system C comprises formulas taken from a decidable SMT logic [2], including, for example, linear arithmetic constraints and uninterpreted predicates. The Object Constraint System O (C) introduces the constraints: • class (C), which it true for all classes C defined in the program; • x hasImm F, to denote that the immutable field F is accessable from variable x; • x hasMut G, to denote that the mutable field G is accessable from variable x; and • fields (x) = ♦F, G, to expose all fields available to x. Figure 1 shows the constraint system as ported from CFG [3]. We refer the reader to that work for details. The main differences are syntactic changes to account for our notion of strengthening. Also the FIELD rule accounts now for both immutable (as in CFJ) and mutable fields.