WEBVTT 1 00:00:07.850 --> 00:00:10.740 >> Welcome to the Haskell Weekly podcast. This is a show 2 00:00:10.740 --> 00:00:13.130 about Haskell, a purely functional programming 3 00:00:13.130 --> 00:00:16.030 language. I'm your host, Taylor Fausak, the 4 00:00:16.030 --> 00:00:18.550 lead engineer at ITProTV, an ACI 5 00:00:18.820 --> 00:00:21.460 learning company. With me today is Cameron 6 00:00:21.460 --> 00:00:24.400 Gera, one of the engineers on my team. Thanks for joining me 7 00:00:24.400 --> 00:00:25.150 today, Cam. 8 00:00:25.160 --> 00:00:27.720 >> Thanks for having me, Taylor. Pleasure as 9 00:00:27.720 --> 00:00:30.560 always I'm just really excited about today. I 10 00:00:30.560 --> 00:00:33.260 think we've got some great content ahead of us 11 00:00:33.270 --> 00:00:36.070 going to be talking a little bit about a 12 00:00:36.070 --> 00:00:39.070 language extension called type applications. So, 13 00:00:39.080 --> 00:00:41.850 uh, if you're familiar with Haskell, you've probably heard of type 14 00:00:41.850 --> 00:00:44.800 applications. If you're new to Haskell, well 15 00:00:44.800 --> 00:00:47.720 then you're in for a special treat today. We're gonna kind of walk 16 00:00:47.720 --> 00:00:50.700 through type applications. You know what? What's helpful 17 00:00:50.700 --> 00:00:53.650 about it? What's, you know, maybe confusing about 18 00:00:53.650 --> 00:00:56.410 it and really dive in to a 19 00:00:56.410 --> 00:00:58.860 post that Zach Wood, uh, 20 00:00:59.240 --> 00:01:02.100 wrote called Haskell's at 21 00:01:02.110 --> 00:01:05.060 symbol type applications. So, 22 00:01:05.070 --> 00:01:07.800 uh, to kick off, 23 00:01:07.810 --> 00:01:10.720 he I think, probably works 24 00:01:10.720 --> 00:01:13.570 with, uh, IHP, which is integrated 25 00:01:13.570 --> 00:01:16.160 Haskell platform. And he is trying 26 00:01:16.160 --> 00:01:18.990 to help explain, um, some of 27 00:01:18.990 --> 00:01:21.330 the extensions that are 28 00:01:21.340 --> 00:01:24.280 uh, kind of on by default 29 00:01:24.280 --> 00:01:27.260 when you're using the the IHP platform. You know, uh, 30 00:01:27.640 --> 00:01:30.330 framework, I believe, is really what it is at the end of the 31 00:01:30.330 --> 00:01:32.660 day. Um and 32 00:01:32.660 --> 00:01:35.610 so, yeah, tell us a little bit about 33 00:01:35.620 --> 00:01:36.960 type applications. Taylor. 34 00:01:37.940 --> 00:01:40.870 >> Yeah. For context. Like you mentioned, 35 00:01:40.870 --> 00:01:43.600 the I H P is a framework for building Web 36 00:01:43.600 --> 00:01:46.490 applications with Haskell. And if you're familiar with Ruby on 37 00:01:46.490 --> 00:01:49.380 rails, I think it tries to be a lot like that. So 38 00:01:49.390 --> 00:01:51.760 it aims to be very developer friendly, 39 00:01:52.140 --> 00:01:54.930 and one of the things that you often want to 40 00:01:54.930 --> 00:01:57.670 do with Haskell is have a function that is 41 00:01:57.670 --> 00:01:59.940 polymorphic that could be used in a lot of different 42 00:01:59.940 --> 00:02:02.690 contexts. But then you need to pick which 43 00:02:02.690 --> 00:02:05.520 context you're using it in. So the example he gives is if you're 44 00:02:05.520 --> 00:02:07.650 like, querying for something from the database, 45 00:02:08.140 --> 00:02:10.810 that function should clearly allow you 46 00:02:10.810 --> 00:02:13.390 to query for many different types of 47 00:02:13.390 --> 00:02:16.160 things. Let's say like a user or an 48 00:02:16.160 --> 00:02:18.580 episode for us. That's one of our data models. 49 00:02:18.590 --> 00:02:21.480 Um, but you are gonna wanna pick 50 00:02:21.490 --> 00:02:24.060 which thing you're querying for, so that's where type 51 00:02:24.060 --> 00:02:26.970 applications can come in as a solution to that problem where you have this 52 00:02:26.970 --> 00:02:29.960 polymorphic function, you say I want to use it with 53 00:02:29.970 --> 00:02:31.360 this specific type. 54 00:02:31.840 --> 00:02:34.460 >> Yeah, and you know, I think type 55 00:02:34.460 --> 00:02:37.410 applications is a great way to fix this one 56 00:02:37.420 --> 00:02:40.340 for us. We actually had this 57 00:02:40.340 --> 00:02:43.180 kind of similar problem where we had a query that could return 58 00:02:43.190 --> 00:02:45.800 all kinds of different things. And if we didn't use it in another 59 00:02:45.800 --> 00:02:48.350 context, it couldn't figure out. You know 60 00:02:48.840 --> 00:02:51.570 what type we were trying to query there. So we 61 00:02:51.570 --> 00:02:54.130 actually used to do just kind of type 62 00:02:54.130 --> 00:02:56.440 assertion at the variable 63 00:02:56.440 --> 00:02:59.310 Declaration. So that was 64 00:02:59.320 --> 00:03:01.890 you know, all right, we have user 65 00:03:01.900 --> 00:03:04.850 whose colon colon type user and then that's 66 00:03:04.850 --> 00:03:07.340 bound from the query that we were running. 67 00:03:07.340 --> 00:03:10.180 So you know, that's why another way to 68 00:03:10.190 --> 00:03:12.570 do what type application does 69 00:03:13.270 --> 00:03:16.190 >> and funny note about that that requires a 70 00:03:16.190 --> 00:03:19.080 different language extension called scoped 71 00:03:19.090 --> 00:03:22.010 type variables, to be able to give a 72 00:03:22.010 --> 00:03:24.890 type signature when you bind a variable so either on the 73 00:03:24.890 --> 00:03:27.850 left side of one of the arrows in do notation or 74 00:03:27.850 --> 00:03:30.650 on the left side of unequal sign in a let statement. 75 00:03:31.040 --> 00:03:33.960 Otherwise you have to either give the 76 00:03:33.960 --> 00:03:36.910 type signature on some other line later 77 00:03:36.910 --> 00:03:39.900 in the function where use the thing or on the right 78 00:03:39.900 --> 00:03:42.540 side, you would give, like colon colon, like io 79 00:03:42.540 --> 00:03:45.480 user or the type of the whole expression where 80 00:03:45.480 --> 00:03:47.960 the thing comes from rather than just that piece you care about. 81 00:03:48.540 --> 00:03:51.530 >> Yeah. True. True. True. Yeah, thank you for that correction. But 82 00:03:51.530 --> 00:03:54.400 yeah, that was also something we used to do before we even 83 00:03:54.400 --> 00:03:56.490 had scope type variables. So 84 00:03:56.500 --> 00:03:59.250 yeah, I think type applications 85 00:03:59.940 --> 00:04:02.840 cleaned up the code a little bit over scope type 86 00:04:02.840 --> 00:04:05.560 variables because, you know, we 87 00:04:05.560 --> 00:04:08.510 could kind of read the functional, revered 88 00:04:08.510 --> 00:04:11.340 writing and then say, Oh, hey, here's what type that 89 00:04:11.350 --> 00:04:14.300 thing needs to return Or here's that, really. 90 00:04:14.310 --> 00:04:17.260 Here's that type that needs to be filled into the polymorphic 91 00:04:17.270 --> 00:04:18.750 piece of this function. 92 00:04:19.140 --> 00:04:22.130 >> Yeah, and one of the reasons I think that we 93 00:04:22.140 --> 00:04:24.870 didn't use type applications or scoped type 94 00:04:24.870 --> 00:04:27.820 variables for a while is that in general, I try to avoid 95 00:04:27.820 --> 00:04:30.730 using language extensions, but these ones, we had 96 00:04:30.730 --> 00:04:33.710 enough polymorphic functions where the 97 00:04:33.710 --> 00:04:36.710 utility was just undeniable. And instead of 98 00:04:36.710 --> 00:04:39.390 ending up writing like a find 99 00:04:39.390 --> 00:04:42.290 user function and find episode function and find 100 00:04:42.290 --> 00:04:44.810 this, find that you just have one find 101 00:04:44.810 --> 00:04:47.760 function and you pass the at type name for 102 00:04:47.760 --> 00:04:50.460 the next thing. And it feels like you get a lot of the same 103 00:04:50.460 --> 00:04:53.260 benefits as if you had a lot of different monomorphic 104 00:04:53.260 --> 00:04:53.860 functions, 105 00:04:54.340 --> 00:04:57.120 >> right? Right. And you know, I mean, I 106 00:04:57.130 --> 00:05:00.080 know you. The habit is to shy away from 107 00:05:00.080 --> 00:05:02.900 a language extension before, you know, going to it 108 00:05:02.910 --> 00:05:05.910 until you see that use case. And I think for us, we really 109 00:05:05.920 --> 00:05:08.680 did find that use case, Uh, you know, and 110 00:05:08.690 --> 00:05:11.550 the nice thing about type applications as a language extension is 111 00:05:11.560 --> 00:05:14.450 it's pretty well known around the community. And, you know, 112 00:05:14.740 --> 00:05:17.620 it's even gonna be in the release of GHT 2021 which 113 00:05:17.620 --> 00:05:20.540 we've talked about in previous podcast. So you know, there's 114 00:05:20.550 --> 00:05:23.460 ah lot of community understanding on 115 00:05:23.460 --> 00:05:26.320 tap type applications and you know, it's 116 00:05:26.320 --> 00:05:29.320 something. There's a lot of, you know, tutorials on 117 00:05:29.320 --> 00:05:32.210 what it does and how it works. Um, you know, and 118 00:05:32.220 --> 00:05:34.760 this post is another opportunity to kind of 119 00:05:35.140 --> 00:05:37.960 show what power it has. Um, 120 00:05:38.340 --> 00:05:41.060 but, you know, we've been praising type applications a 121 00:05:41.060 --> 00:05:43.810 lot, but I know there is one thing that's kind 122 00:05:43.810 --> 00:05:46.140 of tricky when it comes to type 123 00:05:46.140 --> 00:05:49.090 applications. And that's what like 124 00:05:49.100 --> 00:05:50.860 when you put in that symbol in some 125 00:05:51.240 --> 00:05:53.920 type, you think it may be a 126 00:05:53.920 --> 00:05:56.050 variable to the function when it's really not, 127 00:05:56.060 --> 00:05:57.180 Uh, 128 00:05:57.190 --> 00:06:00.030 >> it's gonna be really confusing, because, uh, the 129 00:06:00.030 --> 00:06:02.960 at sign you might think it could be used as an 130 00:06:02.960 --> 00:06:05.720 operator. So if you had some identify 131 00:06:05.720 --> 00:06:08.720 at sign some, some other identify that 132 00:06:08.720 --> 00:06:11.580 could be a normal operator call like, plus or you know, 133 00:06:11.590 --> 00:06:14.550 something like that. But it actually it can't be in 134 00:06:14.550 --> 00:06:17.060 Haskell because the at sign is reserved for this 135 00:06:17.060 --> 00:06:19.770 special thing when you bind 136 00:06:19.770 --> 00:06:22.500 variables or when you match on them. So, like if you want to 137 00:06:22.500 --> 00:06:25.370 match on a list and destructure the 138 00:06:25.370 --> 00:06:28.370 head and the tail using colon, but you wanna 139 00:06:28.370 --> 00:06:31.370 hang on to that overall list, you can do that with the at sign 140 00:06:31.370 --> 00:06:33.900 so you do the like whole 141 00:06:33.900 --> 00:06:36.410 term on the left and then at sign and 142 00:06:36.410 --> 00:06:39.080 then some destructuring pattern on the 143 00:06:39.080 --> 00:06:41.250 right. Um, so 144 00:06:41.640 --> 00:06:44.420 that's one way that type applications could be a little 145 00:06:44.420 --> 00:06:46.590 confusing is that this at sign is overloaded. 146 00:06:46.600 --> 00:06:49.440 But fortunately, uh, the like 147 00:06:49.440 --> 00:06:51.900 space around the operator is what 148 00:06:51.910 --> 00:06:54.780 disambiguates it. So if you have a space before the at 149 00:06:54.780 --> 00:06:57.450 sign, you know that it's gonna be a type application, 150 00:06:58.240 --> 00:07:01.210 >> right? And then, yeah, I mean, and that's that's one 151 00:07:01.210 --> 00:07:04.090 thing. The other thing, too, is you know, the order 152 00:07:04.100 --> 00:07:06.940 of passing these type types through type 153 00:07:06.940 --> 00:07:09.640 applications matters because, you know, if there's 154 00:07:09.640 --> 00:07:12.360 multiple polymorphic variables in a function, 155 00:07:12.940 --> 00:07:15.550 you have to make sure you pass this in order or you probably 156 00:07:15.550 --> 00:07:18.550 get I mean, I imagine the compiler 157 00:07:19.540 --> 00:07:22.430 errors were pretty helpful, but it could still be pretty confusing, 158 00:07:22.430 --> 00:07:22.990 so 159 00:07:23.000 --> 00:07:25.550 >> they might be pretty gnarly, especially if you have 160 00:07:25.560 --> 00:07:28.540 types of different kinds. So, like 161 00:07:28.540 --> 00:07:31.450 if one of your type arguments is meant to be 162 00:07:31.450 --> 00:07:34.060 some monad, so it takes another type as an argument, 163 00:07:34.440 --> 00:07:37.350 and you try to pass something like into that the kinds 164 00:07:37.350 --> 00:07:40.210 aren't going to match up. And I think most Haskell programmers probably 165 00:07:40.210 --> 00:07:42.810 don't run into that type of error very often, so it might be a little 166 00:07:42.810 --> 00:07:45.720 mystifying. Um, but yeah, the 167 00:07:45.720 --> 00:07:47.920 order of the argument is important, and 168 00:07:47.930 --> 00:07:50.890 usually the order that type 169 00:07:50.890 --> 00:07:53.710 variables appear in a type signature is 170 00:07:53.710 --> 00:07:56.660 OK like that's the order that you would want to supply them, 171 00:07:57.040 --> 00:07:59.970 but sometimes it's not right. You want to 172 00:07:59.970 --> 00:08:01.660 change the order. So how would you do that? 173 00:08:02.740 --> 00:08:05.540 >> Yeah, so that's our good 174 00:08:05.540 --> 00:08:08.110 friend, the for all statement, right? Isn't that thing 175 00:08:08.120 --> 00:08:09.760 >> yet? Another language extension? 176 00:08:10.140 --> 00:08:13.050 >> Yeah. Which we don't tend to 177 00:08:13.050 --> 00:08:15.920 use it very often on our day today. So for me, that's 178 00:08:15.930 --> 00:08:18.740 a little fuzzy. So I'm gonna actually bounce that back to you and 179 00:08:18.740 --> 00:08:20.400 ask Sure about it 180 00:08:20.410 --> 00:08:23.290 >> So the way that I like to think 181 00:08:23.290 --> 00:08:25.940 about for all is sort of a type 182 00:08:25.940 --> 00:08:28.780 level lambda. I think pretty much any Haskell 183 00:08:28.780 --> 00:08:31.570 programmer is gonna be comfortable writing a lambda with a 184 00:08:31.570 --> 00:08:33.460 bunch of variables and then an arrow. 185 00:08:33.940 --> 00:08:36.840 And for me for all is 186 00:08:36.840 --> 00:08:39.340 kind of the same thing on the type level, where you 187 00:08:39.340 --> 00:08:42.200 have the for all and then a bunch 188 00:08:42.200 --> 00:08:45.100 of type variables and then a period. And then you have the type 189 00:08:45.100 --> 00:08:47.690 signature after that. So it's a way 190 00:08:47.690 --> 00:08:50.690 of explicitly listing all the type variables you're 191 00:08:50.690 --> 00:08:53.360 going to use so that you can give them in a particular order. 192 00:08:54.640 --> 00:08:55.760 >> Mhm. Okay, 193 00:08:57.910 --> 00:09:00.720 I knew it was a thing in Haskell, but I didn't really 194 00:09:00.720 --> 00:09:03.180 ever understand the reasoning for it, 195 00:09:03.190 --> 00:09:05.740 Um, way generally don't have 196 00:09:05.750 --> 00:09:08.650 super overly polymorphic functions where we have tell. 197 00:09:09.040 --> 00:09:12.030 Yeah, and where the order always matters or something along 198 00:09:12.030 --> 00:09:14.560 those lines. So for us, 199 00:09:14.940 --> 00:09:17.480 you know, we haven't really run into that too much 200 00:09:17.490 --> 00:09:18.120 personally. 201 00:09:18.130 --> 00:09:21.110 >> Yeah, and it's kind of funny because the four 202 00:09:21.110 --> 00:09:24.020 all is actually always there. It's 203 00:09:24.020 --> 00:09:27.020 just implied that if you mention a type variable and 204 00:09:27.020 --> 00:09:29.920 you haven't quantified it, if you haven't 205 00:09:29.920 --> 00:09:32.530 given it by using one of these for all things, 206 00:09:32.540 --> 00:09:35.340 then ghd will just do that for you. And 207 00:09:35.340 --> 00:09:38.170 sometimes you'll see this on an error message where it'll print out a 208 00:09:38.170 --> 00:09:41.170 type signature and we'll have a four all there. But it's not actually in 209 00:09:41.170 --> 00:09:43.620 your source code, and you may wonder, where did that come from? 210 00:09:43.980 --> 00:09:46.240 Ghd Just put it in there for you. It's 211 00:09:46.240 --> 00:09:49.170 >> magic, you know, feel like today we could even talked 212 00:09:49.170 --> 00:09:52.010 about G 9.0 point 213 00:09:52.010 --> 00:09:54.910 one being released to know we have Yeah, it's got 214 00:09:54.910 --> 00:09:55.450 that 215 00:09:55.460 --> 00:09:58.220 >> got some fancy type stuff in there, but maybe we should do a 216 00:09:58.220 --> 00:10:00.170 whole whole separate episode on that one. There's a lot 217 00:10:00.170 --> 00:10:03.020 >> of time. That's where you're interested in. 218 00:10:03.030 --> 00:10:05.990 It's out there, just, you know. Ah, friendly, Haskell 219 00:10:05.990 --> 00:10:08.810 reminder for those who want to dive on into 220 00:10:08.810 --> 00:10:09.250 that, 221 00:10:09.640 --> 00:10:12.170 >> I mean, I just assume people are already reading the 222 00:10:12.170 --> 00:10:14.850 newsletter right there. Already subscribed to the Haskell 223 00:10:14.850 --> 00:10:17.570 weekly newsletter. I 224 00:10:17.580 --> 00:10:18.050 mean, 225 00:10:18.640 --> 00:10:20.910 >> if you're not, I would definitely go do it now. 226 00:10:20.920 --> 00:10:23.900 It's just an email once a week. That's it. You don't 227 00:10:23.900 --> 00:10:26.610 get too much information. It's not like he's We're trying to 228 00:10:26.610 --> 00:10:29.360 sell you anything. Just trying to show you some 229 00:10:29.360 --> 00:10:30.400 Haskell love, man. 230 00:10:30.410 --> 00:10:33.390 >> Yeah, but on the topic of type applications, is there 231 00:10:33.390 --> 00:10:34.870 anything else you wanted to cover here? 232 00:10:34.880 --> 00:10:37.150 >> Uh, yeah. So, 233 00:10:37.540 --> 00:10:38.260 um, 234 00:10:40.140 --> 00:10:42.870 what else did I want to say? I wanted to say 235 00:10:42.870 --> 00:10:45.750 something, but now I'm forgetting, which is great. Uh, 236 00:10:45.760 --> 00:10:48.740 do you have anything you want to add? Because 237 00:10:48.740 --> 00:10:51.460 I'm blanking at the moment. It's Friday afternoon, everybody. I'm 238 00:10:51.460 --> 00:10:51.980 sorry. 239 00:10:51.990 --> 00:10:54.660 >> Yeah. So we talked about some other 240 00:10:54.670 --> 00:10:57.510 ways that we did stuff that type application 241 00:10:57.510 --> 00:11:00.460 could do for us. So, like scope type variables, they're just manually giving a 242 00:11:00.460 --> 00:11:03.140 type signature. One other very common 243 00:11:03.140 --> 00:11:06.140 pattern that type applications replaces 244 00:11:06.150 --> 00:11:08.780 is passing around proxy arguments. 245 00:11:08.790 --> 00:11:11.690 So if you're not familiar, proxy is a data 246 00:11:11.690 --> 00:11:13.160 type that 247 00:11:14.240 --> 00:11:17.050 doesn't convey any information at the value 248 00:11:17.050 --> 00:11:19.780 level. All of its information is in the type level. 249 00:11:19.790 --> 00:11:22.760 So if you wanted to pass like the 250 00:11:23.240 --> 00:11:26.120 pass a type to a function, you might do that 251 00:11:26.120 --> 00:11:28.860 with a proxy. This is very common with the servant 252 00:11:28.860 --> 00:11:31.660 library. That's how it passes around all this, a p I stuff and 253 00:11:31.660 --> 00:11:33.940 lets you hold on to that as a value. 254 00:11:33.950 --> 00:11:36.870 Um, but with type applications, you 255 00:11:36.870 --> 00:11:39.780 don't really need to use proxy at all. 256 00:11:39.790 --> 00:11:42.550 You can replace that with an explicit type application. So that's 257 00:11:42.550 --> 00:11:44.850 nice. You just get rid of this concept altogether. 258 00:11:45.340 --> 00:11:47.950 >> Yeah. I mean, for me, it's not. I mean, 259 00:11:49.140 --> 00:11:52.090 I'm all for type applications. I think it's been a great quality of 260 00:11:52.090 --> 00:11:54.560 life improvement for our code base. 261 00:11:54.570 --> 00:11:57.540 Um, and as a, you know, engineer 262 00:11:57.550 --> 00:12:00.310 helps me work faster and more 263 00:12:00.320 --> 00:12:02.760 effectively. Um, and also 264 00:12:02.760 --> 00:12:05.730 read code faster for the obviously. At first 265 00:12:05.730 --> 00:12:08.560 it was really weird. I remember the engineer who 266 00:12:08.560 --> 00:12:11.530 kind of like all about it. Cody, he was like, Hey, 267 00:12:11.900 --> 00:12:14.460 let's do this. And I read that PR and I was just like, 268 00:12:15.940 --> 00:12:18.000 Okay, I think I get it. 269 00:12:18.010 --> 00:12:20.160 But at that point You know, 270 00:12:20.540 --> 00:12:22.850 >> it takes a minute to wrap your head around, but I think 271 00:12:23.540 --> 00:12:26.330 once you know what it does, 272 00:12:26.340 --> 00:12:29.290 there's not really a downside to this language extension. 273 00:12:29.290 --> 00:12:32.060 Some language extensions have a little bit of give and take. This one is just 274 00:12:32.070 --> 00:12:34.750 give it lets you express something that you weren't able to do 275 00:12:34.750 --> 00:12:36.150 before. Mhm. 276 00:12:36.540 --> 00:12:39.230 >> Yeah, I think it's great. Um, is there anything else from the 277 00:12:39.230 --> 00:12:42.050 Post that you were, uh, you know, interested 278 00:12:42.050 --> 00:12:44.980 in or intrigued you? Because obviously, we talked a 279 00:12:44.980 --> 00:12:47.840 little bit about the post, but not a ton. He was Yeah. 280 00:12:47.850 --> 00:12:50.340 This is a great opportunity for us to have a good jumping off 281 00:12:50.340 --> 00:12:53.150 point. Um, but we didn't really dive too 282 00:12:53.150 --> 00:12:55.160 much into the actual post. 283 00:12:55.540 --> 00:12:58.330 >> Um I mean, it was a great post. I really like 284 00:12:58.330 --> 00:13:01.280 reading. Zach has put out a handful of posts, and I like reading 285 00:13:01.280 --> 00:13:04.250 all of them. Um, this also gave me some good 286 00:13:04.250 --> 00:13:07.060 insight or like, kind of day in the life 287 00:13:07.060 --> 00:13:09.920 slice of life type stuff about I h p. I 288 00:13:09.920 --> 00:13:12.890 haven't used it myself, but I've seen a lot of people excited 289 00:13:12.890 --> 00:13:15.720 about it in the community, and I like what it's trying to do so. I like seeing posts like 290 00:13:15.720 --> 00:13:17.260 this that give me a taste of it. 291 00:13:17.640 --> 00:13:20.590 >> Yeah, I know. I think he's gonna have to do some follow up post, 292 00:13:20.590 --> 00:13:23.520 too, because he's got two other language extension. He's use 293 00:13:23.530 --> 00:13:26.410 in the posts that he actually had comments in the post 294 00:13:26.410 --> 00:13:29.260 about which is really and he was very quick to react. 295 00:13:29.260 --> 00:13:31.690 So I'm sure if you have more questions. I think Zach's got you 296 00:13:33.890 --> 00:13:34.825 >> Exactly. 297 00:13:34.825 --> 00:13:35.760 >> Exactly. 298 00:13:36.140 --> 00:13:39.120 >> Dude you can't escape the puns. I didn't 299 00:13:39.120 --> 00:13:41.890 mean to. Wow, just subconsciously 300 00:13:41.890 --> 00:13:42.760 punning all the time. 301 00:13:43.340 --> 00:13:45.460 >> That's life. 302 00:13:46.140 --> 00:13:49.140 >> Um, but yeah, Cam, like you mentioned, I think next week 303 00:13:49.150 --> 00:13:52.110 we'll have to talk about GH c nine. But I think that will do 304 00:13:52.110 --> 00:13:54.360 it for us this week. Unless you get anything else. 305 00:13:55.240 --> 00:13:57.850 >> I don't think so. I mean, it's a great quick 306 00:13:57.850 --> 00:14:00.360 topic. Um, I mean, 307 00:14:01.040 --> 00:14:03.720 I think the only other thing I was thinking about talking about with 308 00:14:03.720 --> 00:14:06.670 examples of you, but you think we should talk about 309 00:14:06.670 --> 00:14:09.160 some examples like it's really good 310 00:14:10.750 --> 00:14:12.340 >> he gives a couple in the post, right? 311 00:14:12.350 --> 00:14:15.340 >> Right. He uses reading show is a great examples because, you 312 00:14:15.340 --> 00:14:18.250 know, read takes a string and returns today and show takes a 313 00:14:18.250 --> 00:14:21.170 name, returns a string. Uh, you can for the 314 00:14:21.170 --> 00:14:22.560 read function, you could assert it, 315 00:14:23.840 --> 00:14:26.750 or you could always write a wrapper function that 316 00:14:27.440 --> 00:14:30.440 gives it explicit types. But if you don't wanna do that, 317 00:14:30.450 --> 00:14:33.400 you can just type applications to say, Hey, I 318 00:14:33.400 --> 00:14:36.210 want this string 1234 or 1234 319 00:14:36.220 --> 00:14:39.070 to become an int and you just do read 320 00:14:39.080 --> 00:14:41.690 at ent this string. So it'll 321 00:14:41.690 --> 00:14:44.490 transform it and obviously create a run time 322 00:14:44.560 --> 00:14:46.660 error if you can't do that. But 323 00:14:47.640 --> 00:14:50.100 you know it tries which, you know, I think that was a great 324 00:14:50.100 --> 00:14:52.870 example. Some more for us that we 325 00:14:52.870 --> 00:14:55.680 see on a more day to day basis is, you know, 326 00:14:55.690 --> 00:14:58.010 from from integral or 327 00:14:58.010 --> 00:15:00.740 realToFrac to transform one 328 00:15:00.750 --> 00:15:03.350 integral type to another integral type 329 00:15:03.740 --> 00:15:06.320 >> these are Like the Swiss Army knife 330 00:15:06.320 --> 00:15:09.190 conversion functions, they're used for so many things, 331 00:15:09.190 --> 00:15:12.120 like from a machine sized integer into 332 00:15:12.120 --> 00:15:14.940 some specific sized incised, unsigned 333 00:15:14.940 --> 00:15:17.690 integer, or like from a database type 334 00:15:17.690 --> 00:15:20.690 into a normal type or from a time. Or, you 335 00:15:20.690 --> 00:15:23.640 know, just all kinds of things have surprising instances where 336 00:15:23.640 --> 00:15:26.260 you can convert it with from integral on, and 337 00:15:26.840 --> 00:15:29.490 a lot of times I encourage people to write 338 00:15:29.500 --> 00:15:32.320 monomorphic rapper functions like specifically from this 339 00:15:32.320 --> 00:15:35.240 type of that type. But with type applications, you 340 00:15:35.240 --> 00:15:38.040 can say from integral at this type at that 341 00:15:38.040 --> 00:15:41.040 type and then you don't need to write that extra function. You just kind of define 342 00:15:41.040 --> 00:15:42.160 it in line as it were. 343 00:15:42.640 --> 00:15:45.220 >> Yeah, which, you know, pros and 344 00:15:45.220 --> 00:15:48.080 cons. But if you're kind of 345 00:15:48.080 --> 00:15:50.650 familiar with the extension, 346 00:15:51.140 --> 00:15:53.890 I think it's a easy thing to grok. You know, 347 00:15:53.900 --> 00:15:56.690 obviously, if you're new to a code base and you've never seen 348 00:15:56.690 --> 00:15:59.590 type application before, yeah, you would be like wait a second. Why 349 00:15:59.590 --> 00:16:02.410 is this that way? We should just made it a separate function. 350 00:16:02.420 --> 00:16:05.190 >> But that actually reminds me, 351 00:16:05.200 --> 00:16:08.070 um, one thing we didn't touch on yet that I think we should 352 00:16:08.070 --> 00:16:10.500 is that with type applications, 353 00:16:10.510 --> 00:16:13.380 sometimes a function will have, Let's 354 00:16:13.380 --> 00:16:16.000 say, to type variables, and you want 355 00:16:16.000 --> 00:16:18.760 to only supply the second one. So 356 00:16:18.770 --> 00:16:21.610 you're like whatever the first one is. If you want to infer it, 357 00:16:21.620 --> 00:16:24.460 that's fine. But the second one needs to be int, 358 00:16:24.840 --> 00:16:27.560 and you can do that with type applications, where, 359 00:16:27.940 --> 00:16:30.900 instead of saying at some type name you say 360 00:16:30.900 --> 00:16:33.310 at Underscore and that tells G h 361 00:16:33.310 --> 00:16:36.090 c go ahead and do what you were going to do here. Anyway, 362 00:16:36.090 --> 00:16:38.590 Just pretend I'm not here and I'll do the next thing, 363 00:16:38.600 --> 00:16:41.480 >> right? And that's you know where that order matters. Because if you 364 00:16:41.480 --> 00:16:44.360 try to just apply the second one it would infer it as the 365 00:16:44.360 --> 00:16:45.760 first one, right? 366 00:16:47.440 --> 00:16:50.030 >> like with from integral. If if in your 367 00:16:50.030 --> 00:16:52.890 context, the first type variable is already picked for 368 00:16:52.890 --> 00:16:55.770 you. So you don't wanna specify it again, You would 369 00:16:55.770 --> 00:16:58.610 say from integral at underscore at 370 00:16:58.620 --> 00:17:01.150 int. And then that would say, I'm converting into an integer. 371 00:17:01.630 --> 00:17:04.450 >> Right? But that's Yeah, super nice little 372 00:17:04.940 --> 00:17:07.580 thing that type applications 373 00:17:07.590 --> 00:17:10.540 gave us so much. Appreciate it. Thank 374 00:17:10.540 --> 00:17:12.890 you, programmers. Who created this? 375 00:17:12.900 --> 00:17:15.850 >> Great. Yeah, that's a good one. 376 00:17:16.340 --> 00:17:19.220 Uh, so, yeah, I feel like we've we've 377 00:17:19.220 --> 00:17:22.170 said we're almost done for a couple times here, but I think we're actually almost done now. 378 00:17:22.180 --> 00:17:25.080 >> Yeah, I think so. I mean, you know, I wanted to give us 379 00:17:25.080 --> 00:17:27.300 some good content. I was like, What? We need 380 00:17:27.300 --> 00:17:29.830 examples, So yeah, Glad we got that 381 00:17:29.840 --> 00:17:32.670 opportunity. Sorry, but yeah, the emotional roller 382 00:17:32.670 --> 00:17:34.980 coaster off our listeners. 383 00:17:34.990 --> 00:17:37.460 >> Are we over? Are we not? We were over. 384 00:17:38.140 --> 00:17:41.000 Thank you. Okay. No, no, there's no more. 385 00:17:41.010 --> 00:17:43.890 Uh, yeah. Thank you for listening to the high 386 00:17:43.890 --> 00:17:46.860 school weekly podcast. I have been your host, Taylor Fausak. 387 00:17:46.860 --> 00:17:49.820 And with me today was Cameron Gera. If you want to find 388 00:17:49.820 --> 00:17:52.750 out more about Haskell Weekly, you can go to our website 389 00:17:52.760 --> 00:17:55.530 haskellweekly.news And if you 390 00:17:55.530 --> 00:17:58.390 enjoyed the show, please rate and review us on apple 391 00:17:58.390 --> 00:18:00.990 podcasts. And if you have any feedback for us, 392 00:18:01.000 --> 00:18:03.350 tweet us at Haskell Weekly 393 00:18:04.540 --> 00:18:07.420 >> And Haskell Weekly is brought to you by ITProTV and 394 00:18:07.420 --> 00:18:10.170 A C I learning company and our employer. 395 00:18:10.180 --> 00:18:13.170 They would like to offer you 30% off your 396 00:18:13.170 --> 00:18:14.860 subscription by using promo code 397 00:18:14.870 --> 00:18:17.410 HASKELLWEEKLY30 at check 398 00:18:17.410 --> 00:18:20.260 out. And that about does it for us, huh? Taylor? 399 00:18:20.740 --> 00:18:21.670 >> Sure does. 400 00:18:22.140 --> 00:18:24.895 >> Well, thanks for joining us this week on Haskell Weekly, and 401 00:18:25.630 --> 00:18:26.760 we'll see you next week. 402 00:18:27.540 --> 00:18:28.050 >> Bye.