( c a l l / c c ( l a m b d a ( c o n t ) ( c o n t ஌ ݟ ) ) ) 2 0 1 5 ೥ 1 0 ݄ 1 8 ೔ ୈ 2 ճ O U C C LT ձ

͓ · ͑ ͔ • ͢͢͠ • ΞϨܥ • űwiűűer: @susisu2413 • GitHub: susisu • Scheme ૉਓͰ͢

ܧ ଓ • "ܧଓʢ͚͍ͧ͘ɺcontinuationʣͱ͸ɺϓϩάϥϜͷ ࣮ߦʹ͓͍ͯ͋Δ࣌఺ʹ͓͍ͯධՁ͞Ε͍ͯͳ͍࢒Γ ͷϓϩάϥϜʢthe rest of the programʣΛҙຯ͢Δ΋ ͷͰ͋Γɺखଓ͖ʢprocedureʣͱͯ͠දݱ͞ΕΔ΋ ͷͰ͋Δɻ" ܧଓ - Wikipedia https://ja.wikipedia.org/wiki/ %E7%B6%99%E7%B6%9A

ࡴ െ ͱ ͠ ͨ εϥ Π υ ʹ S ࣜ ͕ (+ 1 2)

2 ͔ Β ݟ ͨ ܧ ଓ (+ 1 (...))

ϥϜ μ ࣜ Ͱ ͸ (lambda (x) (NEXT (+ 1 x) )) NEXT ͸ͦ͜ͰධՁΛऴྃ͢ΔԾ૝ͷॲཧ

c a l l / c c • ུͣ͞ʹݴ͏ͱ call-with- current-continuation • ݱࡏͷܧଓΛҾ਺ͱͯ͠, ༩͑ΒΕͨؔ਺Λݺͼग़͢ • ܧଓ͸ͨͩͷؔ਺ͳͷͰ, อଘ͓͍ͯͯ͠, ผͷ৔ॴ ͔Βݺͼग़͢͜ͱ΋Մೳ

(+ 1 2)

2 Λ c a l l / c c ͷ ࣜ Ͱ ஔ ͖ ׵ ͑ͯ Έ Δ (+ 1 (call/cc (lambda (cont) (cont 2)) ))

c a l l / c c ͷ Ҿ ਺ ( ؔ ਺ ) ʹ ౉ ͞ Ε Δ ܧ ଓ (+ 1 (...))

ϥϜ μ ࣜ Ͱ ͸ (lambda (x) (NEXT (+ 1 x) ))

ͭ · Γ ͜͏ ͍ ͏ ͜ ͱ (+ 1 ( (lambda (cont) (cont 2)) (lambda (x) (NEXT ( (+ 1 x) ))) ))

ධ Ձ Λ ਐ Ί Δ (+ 1 (NEXT (+ 1 2) ))

Կ ʹ ࢖ ͑Δ ͷ ͔ • ϧʔϓ୤ग़ (break) • ྫ֎ॲཧ (throw) • ίϧʔνϯ (yield) • return, goto, etc. • ཁ͸ಥೖͱ୤ग़

ͭΑ ͍

࣮ ૷ ͠ ͨ

Ͳ ͏ ͍ ͏ ࣮ ૷ • https://github.com/susisu/js-sandbox/blob/master/ continuation/src/v2.js • AST ΠϯλϓϦλ in JavaScript • جૅ͸લճͷ LT Ͱൃදͨ͠΋ͷͷྲྀ༻ http://susisu.hatenablog.com/entry/2015/07/12/142250 • Scheme ͷྫΛ͍͔ͭ͘ࢼͨ͠ͱ͜Ζظ଴௨Γʹಈ࡞ͨ͠ ͷͰɺͨͿΜ্ख͍͍ͬͯ͘Δ

ܧ ଓ ͷ ੜ ੒ ( ୯ ७ Խ ͠ ͨ ΋ ͷ ) • ࣜ Expr • ࣜͷධՁ eval : Expr → Res ― ݫີʹ͸؀ڥ΋ඞཁ • ධՁ݁Ռ Res = Ok Val ― ੒ޭ | Cont Val (Res → Res) ― ܧଓ | Next Val ― ධՁऴྃ

ܧ ଓ ͷ ੜ ੒ • ྫ͑͹ɺෳ਺ͷࣜΛॱ൪ʹධՁ͢ΔΑ͏ͳࣜ e = (e1 : Expr, e2 : Expr, ..., eN : Expr) : Expr r = eval e, ri = eval ei ― ධՁ݁Ռ • ri = Ok v 㱺 ei+1 Ҏ߱ͷධՁΛଓ͚Δ, i = N ͳΒ͹ r = Ok v • Cont f c 㱺 r = Cont f ((λx → eval ([r1 , ..., ri-1 ,] x, ei+1 , ..., eN )) ○ c) • Next v 㱺 r = Next v

ܧ ଓ ͷ ੜ ੒ • τοϓϨϕϧʹ͸த਎ͷࣜͷධՁ݁Ռ͕ Ok v ͳΒ͹ Next v ͱͳΔࣜΛஔ͍͓ͯ͘ • eval “(call/cc f)” = Cont f (λx → x) • (call/cc f) ΛؚΉࣜΛධՁ͢Δͱ Cont f c ͕ಘΒΕΔ • ࠷ޙʹ c (f c) Λܭࢉ͢Ε͹ (ͦͷ͏ͪ) ஋͕ग़ͯ͘Δ

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D E M O

ܧ ଓ ͸ ྗ