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This channel is intended for people just starting with the Raku Programming Language (raku.org). Logs are available at irclogs.raku.org/raku-beginner/live.html Set by lizmat on 8 June 2022. |
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| habere-et-disper | Hello everyone \o/ | 08:06 | |
| I have a working recursion whose implicit base case I don't understand. Too much DWIM -- but then that kind of magic is why I adore raku. Would a rakoon care to unravel it for me? I can post a link or we can try here. :) | |||
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| dakkar | habere-et-disper: we can try ☺ give us the link | 09:04 | |
| habere-et-disper | How does this recursion terminate? | 09:26 | |
| ~~~raku | |||
| sub to-roman ( $deca, @units = < | |||
| 1000 M 900 CM 500 D 400 CD 100 C 90 XC | |||
| 50 L 40 XL 10 X 9 IX 5 V 4 IV | |||
| 1 I | |||
| >.pairup ) is export { | |||
| .value x $deca div .key | |||
| ~ to-roman $deca mod .key, @units.skip | |||
| with @units.head | |||
| } | |||
| ~~~ | |||
| The final call I think looks something like `to-roman( 0, () )`. This in turn appears to give us: | |||
| ~~~raku | |||
| ().head.value x 0 div ().head.key | |||
| ~ | |||
| to-roman 0 mod ().head.key, ().skip | |||
| ~~~ | |||
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| dakkar | ().head is Nil | 09:27 | |
| therefore, the `with` doesn't execute | |||
| that whole body is `something-something with @units.head` | 09:28 | ||
| lizmat | also, please use a gist :) | ||
| dakkar | if there's no head, nothing happens | ||
| Nemokosch | which makes it work but I'm not sure if I like this design, once again | ||
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| the whole type object/Nil/Empty polemy | 09:30 | ||
| habere-et-disper | Thanks @dakkar! | 09:32 | |
| Nemokosch | you know the funny thing is | 09:33 | |
| the function itself returns Empty on the terminating call xD | 09:34 | ||
| that's why you don't get some horrible warning | |||
| habere-et-disper | Thank you all for the clarity. I had started to think of `with` as more a nautral language word than having an underlying `if`-like construct. | 09:37 | |
| Nemokosch | `with` is like `if defined` plus `given` | 09:42 | |
| habere-et-disper | That's helpful. Thank you discord-raku-bot. :) | 09:45 | |
| dakkar | discord-raku-bot is the name of the… bot, that bridges IRC with Discord | 09:47 | |
| the person's name (in this case) is Nemokosch | 09:48 | ||
| habere-et-disper | I learnt something -- thanks @dakkar. So is there a discord recommendation for raku then? | 09:55 | |
| dakkar | there's a discord server that is bridged here | ||
| raku.org/community/ | 09:56 | ||
| habere-et-disper | Are there any builtin aliases for the topic variable? | 10:13 | |
| lizmat | no | 10:14 | |
| but you can create your own lexically | 10:15 | ||
| for @a -> $foo { } | |||
| dakkar | also `with $something -> $whatever { say $whatever }`, or `given`, or `if`… | 10:27 | |
| (also `my $something := $_` may be useful in some cases?) | 10:30 | ||
| habere-et-disper | I seem to be able to only do it one way round. I take it this is intentional to avoid double parsing? | 10:39 | |
| `with @foo -> $bar { $bar-available }` | |||
| `$bar-unavailable with @foo -> $bar` | |||
| Nemokosch | it is intentional | 10:40 | |
| the former is a pointy block, the latter would be weird as one | 10:41 | ||
| dakkar | different explanation: `with $foo` wants a block | 11:00 | |
| the block may declare parameters (`{…}` is a block, `-> $thing {…}` is a "pointy block" that declares a single scalar positional parameter) | 11:01 | ||
| if the block wants a parameter, the topic gets bound to that | |||
| `with` as a statement modifier (the one you write *after* the statement) does not take a block at all | |||
| so, there's nowhere to declare parameters, in that case | |||
| (same for all other constructs that use the same keyword for their block form and their modifier form) | 11:02 | ||
| Nemokosch | same thing, elaborated a bit better 🙂 | 11:12 | |
| habere-et-disper | Thank you dakkar. So why do I need the final `given` here: | 11:14 | |
| `$phone .= substr: 1 if .chars == 11 and .starts-with: 1 given $phone;` | |||
| Should it not be able to know from the `.=` what I'm dealing with? | |||
| Nemokosch | no - `.=` doesn't set the topic variable. Syntactically, it's mo | 11:16 | |
| re like a "mutating method call" | |||
| however, since that is the case, you may drop `$phone` from the beginning of the line, as tonyo pointed out a while ago | 11:18 | ||
| `.= substr: 1 if .chars == 11 and .starts-with: 1 given $phone;` | |||
| I think you need to omit the whitespace in this case | 11:20 | ||
| `.=substr: 1 if .chars == 11 and .starts-with: 1 given $phone;` | |||
| for whatever reason; I think this does qualify as a bug rather than a feature | |||
| habere-et-disper | What's the term again for significant whitespace? | 11:21 | |
| Nemokosch | I don't know but that sounds good enough for a name 😄 | 11:24 | |
| habere-et-disper | (I think it's free-form or non free-form.) | ||
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| habere-et-disper | The up-to operator has me sometimes confused. Compare: | 21:26 | |
| m: my @array = [ 1, 2, 3 ]; say @array[ 0 .. * ] | |||
| m: my @array = [ 1, 2, 3 ]; say @array[ 0 ..^ * ] | |||
| camelia | (1 2 3) | ||
| habere-et-disper | I was expecting (1 2) on the later, no? | ||
| camelia | (1 2 3) | ||
| gfldex | m: my @array = [ 1, 2, 3 ]; say @array[ 0 ..^ ∞ ] | 21:29 | |
| camelia | (1 2 3) | ||
| gfldex | does that help? :-> | ||
| habere-et-disper | That exhibits the same confusion for me. I was wanting the whole array except the last item and I thought the upto operator was nicer than [ 0 .. *-2 ] | 21:32 | |
| gfldex | `Whatever` is tricky indeed. The linguist was stronger then the computer scientist. | 21:34 | |
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| gfldex | That postcircumfix doesn't produce an infinite list when given `0..Inf` makes it useful. | 21:40 | |
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| habere-et-disper | It seems that to get the upto operator to behave as I expected, you have to first put a limit on the whatever: | 21:45 | |
| m: my @array = [ 1, 2, 3 ]; say @array[ 0 ...^ * > .elems ] | |||
| camelia | (1 2) | ||
| Nemokosch | I think * in ranges is always just Inf | 21:48 | |
| regarding the trickyness: as we have come this far, you may notice that `*-1` is not actually... * minus 1, no matter how strange this sounds | 21:51 | ||
| that is, it's not Inf - 1 | |||
| `*-1` is a WhateverCode, basically a very simple function | |||
| the size of the list is substituted into that function, hence `[0 ..^ *-1]` actually works | 21:53 | ||
| similarly, I think `* > .elems` is also a function - a predicate | 21:55 | ||
| by the way, does `.elems` really work in that context? seems surprising to me | |||
| habere-et-disper | It did for the little test I did. I find this slightly more readable: | 21:56 | |
| m: my @array = [ 1, 2, 3 ]; say @array[ 0 ..^ @array.end ] | |||
| camelia | (1 2) | ||
| Nemokosch | I think `.elems` is actually a gotcha | 21:57 | |
| it acts on the (possibly) unset topic variable, and here is where things go painfully wrong to my taste | |||
| the unset topic variable is `(Any)`, right? Now, when you call `.elems`, it's converted into a list... | 21:59 | ||
| if you hope that list is at least an empty list, you are wrong | |||
| It's a one-element list of the `Any` type object... | |||
| m: dd .list | |||
| > (Any,) | |||
| and consequently | |||
| m: .elems.say | 22:00 | ||
| that's right... 1 | 22:01 | ||
| habere-et-disper | Wow! :0 | 22:08 | |
| I must remember to be more careful with .elems! | |||
| lizmat | hm... number of elems being one, is correct I feel | 22:10 | |
| but that it auto-converts... feels wrong | 22:11 | ||
| m: dd .elems; dd $_ | |||
| camelia | 1 Any $_ = Any |
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| lizmat | Nemokosch: cannot reproduce what you're seeing | ||
| m: dd .list # that's explicitely asking for it to become a list | 22:12 | ||
| camelia | (Any,) | ||
| lizmat | m: dd .list; dd $_ | ||
| camelia | (Any,) Any $_ = Any |
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| lizmat | but that still doesn't change the variable *phew* | ||
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| Nemokosch | .elems is not too explicit | 22:50 | |
| anyway, why would something that isn't even `defined` have elems? and if it doesn't, any non-zero answer cannot be right | |||
| [Coke] | m: say 3.list | 22:53 | |
| camelia | (3) | ||
| [Coke] | m: say 3.list.elems | ||
| camelia | 1 | ||
| Nemokosch | docs.raku.org/routine/elems#(Any)_method_elems | 22:59 | |
| that's the gotcha itself | |||
| even Nil.elems is 1 | 23:01 | ||