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Task/Set/EchoLisp/set.l

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+; use { } to read a set
+(define A { 1 2 3 4 3 5 5}) → { 1 2 3 4 5 } ; duplicates are removed from a set
+; or use make-set to make a set from a list
+(define B (make-set ' ( 3 4 5 6 7 8 8))) → { 3 4 5 6 7 8 }
+(set-intersect A B) → { 3 4 5 }
+(set-intersect? A B) → #t ; predicate
+(set-union A B) → { 1 2 3 4 5 6 7 8 }
+(set-substract A B) → { 1 2 }
+(set-sym-diff A B) → { 1 2 6 7 8 } ; ∆ symmetric difference
+(set-equal? A B) →  #f
+(set-equal? { a b c} { c b a}) → #t ; order is unimportant
+(set-subset? A B) → #f ; B in A or B = A
+(set-subset? A { 3 4 }) → #t
+(member 4 A) → (4 5) ; same as #t : true
+(member 9 A) → #f
+
+; check basic equalities
+(set-equal? A (set-union (set-intersect A B) (set-substract A B))) → #t
+(set-equal? (set-union A B) (set-union (set-sym-diff A B) (set-intersect A B))) → #t
+
+; × : cartesian product of two sets : all pairs (a . b) , a in A, b in B
+; returns a list (not a set)
+(define A { albert simon})
+(define B { antoinette ornella marylin})
+
+(set-product A B)
+→ ((albert . antoinette) (albert . marylin) (albert . ornella) (simon . antoinette) (simon . marylin) (simon . ornella))
+
+; sets elements may be sets
+{ { a b c} {c b a } { a b d}} → { { a b c } { a b d } } ; duplicate removed
+
+; A few functions return sets :
+(primes 10) → { 2 3 5 7 11 13 17 19 23 29 }