Algol68 had this property. Consider STRUCT (INT x, y) z = (1, 2) Here z is a const struct. If you wanted a variable, you'd have to say STRUCT (INT x, y)

Algol68 had this property. Consider STRUCT (INT x, y) z = (1, 2) Here z is a const struct. If you wanted a variable, you'd have to say STRUCT (INT x, y) z; z := (1, 2) or equivalently REF STRUCT (INT x, y) z = LOC STRUCT (INT x, y) := (1, 2) Basically a variable has a REF mode.