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1.4. FD Constraints 11

• Example in the TOY(FD)command level:

Next goal returns true and constrains X and Y to have values in the range [1,10].

TOY(FD)> domain [X,Y] 1 10

yes

Y in 1..10

X in 1..10

Elapsed time: 0 ms.

1.4.3 Relational Constraints

Relational constraints include equality and disequality constraints in the form e¦ e

where ¦ ∈ {#<, #=, #<=, #>=, #>, #\=} and e and e

are either integers, or FD

variables or functional expressions.

(#<)/2, (#=)/2, (#<=)/2, (#>=)/2, (#>)/2, (#\=)/2

• Type declaration:

(#>) :: int → int → bool

(#<) :: int → int → bool

(#>=) :: int → int → bool

(#<=):: int → int → bool

(# =) :: int → int → bool

(#\=) :: int → int → bool

• Deﬁnition: ’#Op A B’, also written in inﬁx notation as ’A #Op B’, where Op

∈ {>, <, >=, <=, =, \ =}, returns true if the imposition of the relation ’A #Op

B’ entails the constraint store.

• Remarks: Inﬁx notation allowed.

• Priorities:

infix 30 #>, #<, #>=, #<= (infix)

infix 20 #=, #\= (infix)

• Example at the TOY(FD) command level:

Next goal returns true and restricts X and Y to have values in the intervals [2,10]

and [1,9] respectively (as a consequence of range narrowing).

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Ascend FD-23R Manual de usuario Pagina 23