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Merge pull request #1132 from urbit/roll-reel-redux

2246b1cpoprox5 years ago

content/docs/hoon/reference/stdlib/2b.md+37

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unifiedsplit

@@ -785,6 +785,19 @@ We can fix this with `|:`:

78524

786```

787

788+If you check the definition of `+mul`, you'll see that it also utilizes this

789+pattern.

790+

791+We can check explicitly what sequence of operations `+reel` performs like this:

792+```

793+> =f |: [l='e_l' r='e_r']

794+ ^- @t

795+ :((cury cat 3) '(' l '*' r ')')

796+> (reel "abcde" f)

797+'(a*(b*(c*(d*(e*e_r)))))'

798+```

799+

800+

788---

801---

789

802

790## `++roll`

803## `++roll`

@@ -863,6 +876,30 @@ We can fix this with `|:`:

863> (roll `(list @)`~[1 2 3 4] |:([a=1 b=1] (mul a b)))

876> (roll `(list @)`~[1 2 3 4] |:([a=1 b=1] (mul a b)))

86424

87724

865```

878```

879+If you check the definition of `+mul`, you'll see that it also utilizes this

880+pattern.

881+

882+We can check explicitly what sequence of operations `+roll` performs like this:

883+```

884+> =f |: [l='e_l' r='e_r']

885+ ^- @t

886+ :((cury cat 3) '(' l '*' r ')')

887+> (roll "abcde" f)

888+'(e*(d*(c*(b*(a*e_r)))))

889+```

890+This is in contrast to what one might expect:

891+```

892+> =foldl

893+ |* [l=(list) f=$-([* *] *)]

894+ ^- f

895+ ?~ l +<-.f

896+ %= $

897+ +<-.f (f +<-.f i.l)

898+ l t.l

899+ ==

900+> (foldl "abcde" f)

901+'(((((e_l*a)*b)*c)*d)*e)'

902+```

866

903

867---

904---

868

905