GitHub - rampion/constraint-unions: A syntax for unions of constraints in Haskell

The humble comma. In haskell it does many jobs, for values, types, and constraints. The category theorists will tell you that the simple type (a,b) is a product, justifying the metaphor by if type a has n values, and type b has m values, then type (a,b) has exactly n * m values. The same goes for constraints. The constraint (c,d) is also a product, but since we think of constraints in more binary

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できるもんなら確かにこれは標準で欲しいかも