Read environment variables

Addresses #15

README.md

@@ -7,6 +7,7 @@ Examples showing how to do many things in Gleam!
 - [Data structures](#data-structures)
 - [File system](#file-system)
 - [Formats](#formats)
+- [Operating system](#operating-system)
 
 ## Algorithms
 
@@ -29,3 +30,7 @@ Examples showing how to do many things in Gleam!
 - [Rendering HTML](./universal/test/formats/rendering_html.gleam)
 - [Rendering JSON](./universal/test/formats/rendering_json.gleam)
 - [Rendering XML](./universal/test/formats/rendering_xml.gleam)
+
+## Operating system
+
+- [Read environment variable](./universal/test/operating_system/read_environment_variable.gleam)

universal/gleam.toml

@@ -19,6 +19,7 @@ xmb = ">= 1.0.0 and < 2.0.0"
 gleam_json = ">= 1.0.1 and < 2.0.0"
 lustre = ">= 4.4.4 and < 5.0.0"
 gleam_crypto = ">= 1.3.0 and < 2.0.0"
+envoy = ">= 1.0.1 and < 2.0.0"
 
 [dev-dependencies]
 gleeunit = ">= 1.0.0 and < 2.0.0"

universal/manifest.toml

@@ -2,6 +2,7 @@
 # You typically do not need to edit this file
 
 packages = [
+  { name = "envoy", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "envoy", source = "hex", outer_checksum = "CFAACCCFC47654F7E8B75E614746ED924C65BD08B1DE21101548AC314A8B6A41" },
   { name = "filepath", version = "1.0.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "filepath", source = "hex", outer_checksum = "EFB6FF65C98B2A16378ABC3EE2B14124168C0CE5201553DE652E2644DCFDB594" },
   { name = "gleam_crypto", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_crypto", source = "hex", outer_checksum = "ADD058DEDE8F0341F1ADE3AAC492A224F15700829D9A3A3F9ADF370F875C51B7" },
   { name = "gleam_erlang", version = "0.26.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "3DF72F95F4716883FA51396FB0C550ED3D55195B541568CAF09745984FD37AD1" },
@@ -16,6 +17,7 @@ packages = [
 ]
 
 [requirements]
+envoy = { version = ">= 1.0.1 and < 2.0.0" }
 gleam_crypto = { version = ">= 1.3.0 and < 2.0.0" }
 gleam_json = { version = ">= 1.0.1 and < 2.0.0" }
 gleam_stdlib = { version = ">= 0.34.0 and < 2.0.0" }

universal/test/operating_system/read_environment_variable.gleam

@@ -0,0 +1,40 @@
+//// # Read environment variables
+//// 
+//// The envoy package is used to work with environment variables.  This package 
+//// works on both Erlang and JavaScript targets.
+//// 
+//// Note that we are using `let assert` to crash if any of these functions 
+//// fail.  In a real application or library, you would want to handle results 
+//// properly.
+//// 
+//// ## Dependencies
+//// 
+//// - https://hex.pm/packages/envoy
+//// 
+
+import envoy
+import gleam/dict
+
+pub fn main_test() {
+  // First, unset the PORT variable.  
+  //
+  // We do this fist to get the environment into a known state.  If the PORT
+  // variable is not already set, this will have no effect.
+  let Nil = envoy.unset("PORT")
+
+  // Try to get an environment variable by name.  
+  //
+  // We expect that this will fail, as we unset this variable above.
+  let assert Error(Nil) = envoy.get("PORT")
+
+  // Set the PORT environment variable to 8080.
+  let Nil = envoy.set("PORT", "8080")
+
+  // Now that the PORT variable has been set, we expect to successfully get its
+  // value.
+  let assert Ok("8080") = envoy.get("PORT")
+
+  // We can also get a Dict of all set environment variables.
+  let environment_variables = envoy.all()
+  let assert Ok("8080") = dict.get(environment_variables, "PORT")
+}