Difference between prefix and postfix notation for sum in constraints - why?

[C. G.]

Picat> X::0..1,Y::0..1, Z#=[X,Y].sum.

*** error(instantiation_error,sum)


Picat> X::0..1,Y::0..1, Z#=sum([X,Y]).
X = DV_0139a0_0..1
Y = DV_013a40_0..1
Z = DV_013ac0_0..2
yes

Tested in 3.9.

best regards,

C.G.

[Neng-Fa Zhou]

There is a note in the Users' Guide: "Also note that functions in dot notation are always evaluated eagerly, and therefore should not be used in term constructs or constraint expressions." This design decision does make sense because the dot notation is for chaining function calls, and it's impossible to construct a term with the dot notation.

Cheers,

NF

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