CheatGleam Typed BEAM and JS language
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Start here
gleam new <dir>
Create a project
gleam runCompile and run main
gleam testRun the test suite
gleam add <pkg>
Add a dependency
gleam checkType-check only
gleam formatFormat the code
gleam build --target javascript
Compile to JS
gleam help <cmd>
Show command help
Concepts
- src/*.gleam your modules
- build/ BEAM files or JS
- main() entry point
Projects
gleam new <dir>
Create a new package
--template javascript sets the JS target.
gleam new <dir> --skip-git
Skip .git and .github
--skip-github omits only .github.
gleam runCompile and run main
gleam run --target javascript
Run on the JS target
gleam run --runtime <rt>
JS runtime: nodejs, deno or bun
gleam shellErlang REPL with your code loaded
It speaks Erlang syntax, not Gleam.
gleam cleanDelete the build directory
gleam devRun main of <package>_dev
Build & check
gleam buildCompile package and dependencies
gleam build --target <t>
Pick erlang or javascript
gleam build --warnings-as-errors
Fail on any warning
Handy in CI.
gleam checkType-check without code generation
gleam export erlang-shipment
Directory with bytecode and start script
Test & format
gleam testRun main of <package>_test
gleam test --target <t>
Test on one target
gleam formatFormat the project
gleam format <path>...
Format given files or dirs
gleam format --check
Fail if a file is unformatted
Use it in CI.
Dependencies
gleam add <pkg>
Add latest compatible version
gleam add <pkg>@<version>
Pin a major or full version
Example: gleam add gleam_json@3
gleam add --dev <pkg>
Add as a dev dependency
gleam remove <pkg>
Remove a dependency
gleam deps download
Fetch deps, write manifest.toml
Normally runs automatically.
gleam deps listList all dependency versions
gleam deps outdated
Show dependencies behind latest
gleam deps update [<pkg>...]
Upgrade within gleam.toml limits
Does not edit gleam.toml.
gleam updateAlias for deps update
gleam deps treePrint the dependency tree
gleam deps tree --invert <pkg>
Who depends on this package
Syntax basics
let x = 1Immutable binding
const limit = 10
Top-level constant
Value must be a literal.
x |> f |> g
Pipe into the first argument
case v { 0 -> a _ -> b }
Exhaustive pattern match
[first, ..rest]List pattern or prepend
"pre" <> rest
String prefix pattern, concat
pub type T { A(n: Int) B }
Custom type with variants
Person(..p, age: 30)
Record update
fn f(x: Int, add n: Int) -> Int
Labelled argument
f(1, add:)Label shorthand when names match
use x <- result.try(f())
Flatten callbacks
Rest of the block becomes the callback.
Ok(v) / Error(e)
Result variants
Some(v) / NoneOption, from gleam/option
import gleam/io.{println}
Import module and items
<<1, 2>>
Bit array literal
let assert Ok(v) = r
Crash if the pattern fails
todo as "msg"
Placeholder that crashes if run
assert a == bBoolean check, used in tests
echo valuePrint a debug value
@external(erlang, "m", "f")
Bind to a native function
Publishing & docs
gleam docs build --open
Build HTML docs and open them
gleam publishPublish the package to Hex
gleam publish --replace
Overwrite a release under 1 hour old
gleam hex authenticate
Log in to Hex
gleam docs publish
Publish docs to HexDocs
gleam hex retire --package <p> --version <v>
--reason <r> <msg>
Retire a release
Reasons: other, invalid, security, deprecated, renamed.
gleam hex revert --package <p> --version
<v>
Remove a release within 24 hours
Recipes
gleam new app && cd appgleam add gleam_stdlib gleam_jsongleam add --dev gleeunitgleam testgleam format --checkgleam build --warnings-as-errorsgleam testgleam test --target erlanggleam test --target javascriptpub fn load(id) { use user <- result.try(find(id)) use age <- result.try(parse(user.age)) Ok(age + 1)}Help
gleam helpList all commands
gleam help <command>
Help for one command
gleam --versionPrint the compiler version
gleam lspStart the language server
Editors launch it for you.
