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+Date: Thu, 23 Dec 2021 12:55:31 +0100 (CET)

+From: Prayank <prayank@tutanota.de>

+To: Jeremy <jlrubin@mit.edu>

+Message-ID: <Mrak4sc--7-2@tutanota.de>

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+Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>

+Subject: Re: [bitcoin-dev] [Bitcoin Advent Calendar] Review of Smart

+ Contract Concepts

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+

+------=_Part_67043_1723523109.1640260531416

+Content-Type: text/plain; charset=UTF-8

+Content-Transfer-Encoding: quoted-printable

+

+Hi Jeremy,

+

+> This post covers some high-level smart contract concepts that different

+opcodes or proposals could have (or not).

+https://rubin.io/bitcoin/2021/12/04/advent-7/

+

+Interesting post. I love the concept of recursion in programming. There is =

+one Indian movie called 'Karthik calling Karthik' which is one of the ways =

+I remember this concept.=20

+

+> Recursive is pretty much just a fancy way of saying =E2=80=9Cloops=E2=80=

+=9D. This is sometimesalso called =E2=80=9CTuring Complete=E2=80=9D.

+

+Recently asked one dumb question on Stakexchange after reading a comment on=

+ reddit, maybe you can add anything new in this:

+

+https://bitcoin.stackexchange.com/questions/111337/loops-in-bitcoin-scripti=

+ng

+

+> Here, the contract terminates after one canceled request by moving the co=

+inelsewhere. It=E2=80=99s possible to emulate recursive behavior a limited=

+ amount by=E2=80=9Cunrolling=E2=80=9D a loop.

+

+I think this is what I did in the above link where for loop was replaced wi=

+th if-else statements.

+

+> However, unrolling has it=E2=80=99s limits. When choices(action A or B) a=

+re introduced, unrolling can be less effective since you haveand exponentia=

+l blowup (that means unrolling even like 32 steps might be toomany). Howeve=

+r, there are some tricks that can be employed by a clever andcareful progra=

+mmer to reduce this complexity through, for example, memoization.

+

+Agree with limits and possibility of optimization.

+

+> The key difference being that in the fully enumerated case we must know t=

+he exact specifics of the contract and how it will execute, and in the open=

+ ended contract case there are bits and pieces we can dynamically specify. =

+If Alice is paid 1 BTC by December 25th, 2021 Midnight, then transfer 100 t=

+okensto one of Bob=E2=80=99s Address B1, B2, or B3 at Bob=E2=80=99s discret=

+ion.

+

+Interesting

+

+> Signing the transaction fee rate as a function of locktime

+

+TIL

+

+

+--=20

+Prayank

+

+A3B1 E430 2298 178F

+

+------=_Part_67043_1723523109.1640260531416

+Content-Type: text/html; charset=UTF-8

+Content-Transfer-Encoding: quoted-printable

+

+<html>

+ <head>

+ <meta http-equiv=3D"content-type" content=3D"text/html; charset=3DUTF-8=

+">

+ </head>

+ <body>

+<div>Hi Jeremy,<br></div><div dir=3D"auto"><br></div><div dir=3D"auto">&gt;=

+ This post covers some high-level smart contract concepts that different<br=

+></div><div dir=3D"auto">opcodes or proposals could have (or not).<br></div=

+><div dir=3D"auto">https://rubin.io/bitcoin/2021/12/04/advent-7/<br></div><=

+div dir=3D"auto"><br></div><div dir=3D"auto">Interesting post. I love the c=

+oncept of recursion in programming. There is one Indian movie called 'Karth=

+ik calling Karthik' which is one of the ways I remember this concept. <br><=

+/div><div dir=3D"auto"><br></div><div dir=3D"auto">&gt; Recursive is pretty=

+ much just a fancy way of saying =E2=80=9Cloops=E2=80=9D. This is sometimes

+also called =E2=80=9CTuring Complete=E2=80=9D.<br></div><div dir=3D"auto"><=

+br></div><div dir=3D"auto">Recently asked one dumb question on Stakexchange=

+ after reading a comment on reddit, maybe you can add anything new in this:=

+<br></div><div dir=3D"auto"><br></div><div dir=3D"auto">https://bitcoin.sta=

+ckexchange.com/questions/111337/loops-in-bitcoin-scripting<br></div><div di=

+r=3D"auto"><br></div><div dir=3D"auto">&gt; Here, the contract terminates a=

+fter one canceled request by moving the coin

+elsewhere. It=E2=80=99s possible to emulate recursive behavior a limited a=

+mount by

+=E2=80=9Cunrolling=E2=80=9D a loop.<br></div><div dir=3D"auto"><br></div><d=

+iv dir=3D"auto">I think this is what I did in the above link where for loop=

+ was replaced with if-else statements.<br></div><div dir=3D"auto"><br></div=

+><div dir=3D"auto">&gt; However, unrolling has it=E2=80=99s limits. When ch=

+oices

+(action A or B) are introduced, unrolling can be less effective since you h=

+ave

+and exponential blowup (that means unrolling even like 32 steps might be to=

+o

+many). However, there are some tricks that can be employed by a clever and

+careful programmer to reduce this complexity through, for example, memoizat=

+ion.<br></div><div dir=3D"auto"><br></div><div dir=3D"auto">Agree with limi=

+ts and possibility of optimization.<br></div><div dir=3D"auto"><br></div><d=

+iv dir=3D"auto">&gt; The key difference being that in the fully enumerated =

+case we must know the exact specifics of the contract and how it will execu=

+te, and in the open ended contract case there are bits and pieces we can dy=

+namically specify. If Alice is paid 1 BTC by December 25th, 2021 Midnight, =

+then transfer 100 tokens

+to one of Bob=E2=80=99s Address B1, B2, or B3 at Bob=E2=80=99s discretion.<=

+br></div><div dir=3D"auto"><br></div><div dir=3D"auto">Interesting<br></div=

+><div dir=3D"auto"><br></div><div dir=3D"auto"><div>&gt; Signing the transa=

+ction fee rate as a function of locktime<br></div><div><br></div><div>TIL<b=

+r></div></div><div dir=3D"auto"><br></div><div><br></div><div>-- <br></div>=

+<div>Prayank<br></div><div><br></div><div dir=3D"auto">A3B1 E430 2298 178F<=

+br></div> </body>

+</html>

+

+------=_Part_67043_1723523109.1640260531416--

+