diff --git a/compiler/fmt/src/collection.rs b/compiler/fmt/src/collection.rs
index 3128c4dcf3..40a6f52d24 100644
--- a/compiler/fmt/src/collection.rs
+++ b/compiler/fmt/src/collection.rs
@@ -14,7 +14,7 @@ pub struct CollectionConfig {
 
 pub fn fmt_collection<'a, F: Formattable<'a>>(
     buf: &mut String<'a>,
-    items: Collection<'a, F>,
+    items: Collection<'_, F>,
     indent: u16,
     config: CollectionConfig,
 ) {
diff --git a/compiler/fmt/src/module.rs b/compiler/fmt/src/module.rs
index 3a9a8a495b..43fe1cf9b2 100644
--- a/compiler/fmt/src/module.rs
+++ b/compiler/fmt/src/module.rs
@@ -5,8 +5,8 @@ use crate::spaces::{fmt_default_spaces, fmt_spaces, INDENT};
 use bumpalo::collections::String;
 use roc_parse::ast::{Collection, Module};
 use roc_parse::header::{
-    AppHeader, ExposesEntry, ImportsEntry, InterfaceHeader, PackageEntry, PackageOrPath,
-    PlatformHeader, To,
+    AppHeader, Effects, ExposesEntry, ImportsEntry, InterfaceHeader, ModuleName, PackageEntry,
+    PackageName, PackageOrPath, PlatformHeader, PlatformRequires, PlatformRigid, To, TypedIdent,
 };
 use roc_region::all::Located;
 
@@ -37,7 +37,7 @@ pub fn fmt_interface_header<'a>(buf: &mut String<'a>, header: &'a InterfaceHeade
     fmt_default_spaces(buf, header.before_exposes, " ", indent);
     buf.push_str("exposes");
     fmt_default_spaces(buf, header.after_exposes, " ", indent);
-    fmt_exposes(buf, &header.exposes, indent);
+    fmt_exposes(buf, header.exposes, indent);
 
     // imports
     fmt_default_spaces(buf, header.before_imports, " ", indent);
@@ -77,8 +77,156 @@ pub fn fmt_app_header<'a>(buf: &mut String<'a>, header: &'a AppHeader<'a>) {
     fmt_to(buf, header.to.value, indent);
 }
 
-pub fn fmt_platform_header<'a>(_buf: &mut String<'a>, _header: &'a PlatformHeader<'a>) {
-    todo!("TODO fmt platform header");
+pub fn fmt_platform_header<'a>(buf: &mut String<'a>, header: &'a PlatformHeader<'a>) {
+    let indent = INDENT;
+
+    buf.push_str("platform");
+
+    fmt_default_spaces(buf, header.after_platform_keyword, " ", indent);
+    fmt_package_name(buf, header.name.value);
+
+    // requires
+    fmt_default_spaces(buf, header.before_requires, " ", indent);
+    buf.push_str("requires");
+    fmt_default_spaces(buf, header.after_requires, " ", indent);
+    fmt_requires(buf, &header.requires, indent);
+
+    // exposes
+    fmt_default_spaces(buf, header.before_exposes, " ", indent);
+    buf.push_str("exposes");
+    fmt_default_spaces(buf, header.after_exposes, " ", indent);
+    fmt_exposes(buf, header.exposes, indent);
+
+    // packages
+    fmt_default_spaces(buf, header.before_packages, " ", indent);
+    buf.push_str("packages");
+    fmt_default_spaces(buf, header.after_packages, " ", indent);
+    fmt_packages(buf, header.packages, indent);
+
+    // imports
+    fmt_default_spaces(buf, header.before_imports, " ", indent);
+    buf.push_str("imports");
+    fmt_default_spaces(buf, header.after_imports, " ", indent);
+    fmt_imports(buf, header.imports, indent);
+
+    // provides
+    fmt_default_spaces(buf, header.before_provides, " ", indent);
+    buf.push_str("provides");
+    fmt_default_spaces(buf, header.after_provides, " ", indent);
+    fmt_provides(buf, header.provides, indent);
+
+    fmt_effects(buf, &header.effects, indent);
+}
+
+fn fmt_requires<'a>(buf: &mut String<'a>, requires: &PlatformRequires<'a>, indent: u16) {
+    fmt_collection(
+        buf,
+        requires.rigids,
+        indent,
+        CollectionConfig {
+            begin: '{',
+            end: '}',
+            delimiter: ',',
+        },
+    );
+
+    buf.push_str(" { ");
+    fmt_typed_ident(buf, &requires.signature.value, indent);
+    buf.push_str(" }");
+}
+
+fn fmt_effects<'a>(buf: &mut String<'a>, effects: &Effects<'a>, indent: u16) {
+    fmt_default_spaces(buf, effects.spaces_before_effects_keyword, " ", indent);
+    buf.push_str("effects");
+    fmt_default_spaces(buf, effects.spaces_after_effects_keyword, " ", indent);
+
+    buf.push_str(effects.effect_shortname);
+    buf.push('.');
+    buf.push_str(effects.effect_type_name);
+
+    fmt_default_spaces(buf, effects.spaces_after_type_name, " ", indent);
+
+    fmt_collection(
+        buf,
+        effects.entries,
+        indent,
+        CollectionConfig {
+            begin: '{',
+            end: '}',
+            delimiter: ',',
+        },
+    );
+}
+
+fn fmt_typed_ident<'a>(buf: &mut String<'a>, entry: &TypedIdent<'a>, indent: u16) {
+    use TypedIdent::*;
+    match entry {
+        Entry {
+            ident,
+            spaces_before_colon,
+            ann,
+        } => {
+            buf.push_str(ident.value);
+            fmt_default_spaces(buf, spaces_before_colon, " ", indent);
+            buf.push(':');
+            ann.value.format(buf, indent);
+        }
+        SpaceBefore(sub_entry, spaces) => {
+            fmt_spaces(buf, spaces.iter(), indent);
+            fmt_typed_ident(buf, sub_entry, indent);
+        }
+        SpaceAfter(sub_entry, spaces) => {
+            fmt_typed_ident(buf, sub_entry, indent);
+            fmt_spaces(buf, spaces.iter(), indent);
+        }
+    }
+}
+
+impl<'a> Formattable<'a> for TypedIdent<'a> {
+    fn is_multiline(&self) -> bool {
+        false
+    }
+
+    fn format(&self, buf: &mut String<'a>, indent: u16) {
+        fmt_typed_ident(buf, self, indent);
+    }
+}
+
+impl<'a> Formattable<'a> for PlatformRigid<'a> {
+    fn is_multiline(&self) -> bool {
+        false
+    }
+
+    fn format(&self, buf: &mut String<'a>, indent: u16) {
+        fmt_platform_rigid(buf, self, indent);
+    }
+}
+
+fn fmt_package_name<'a>(buf: &mut String<'a>, name: PackageName) {
+    buf.push_str(name.account);
+    buf.push('/');
+    buf.push_str(name.pkg);
+}
+
+fn fmt_platform_rigid<'a>(buf: &mut String<'a>, entry: &PlatformRigid<'a>, indent: u16) {
+    use roc_parse::header::PlatformRigid::*;
+
+    match entry {
+        Entry { rigid, alias } => {
+            buf.push_str(rigid);
+            buf.push_str("=>");
+            buf.push_str(alias);
+        }
+
+        SpaceBefore(sub_entry, spaces) => {
+            fmt_spaces(buf, spaces.iter(), indent);
+            fmt_platform_rigid(buf, sub_entry, indent);
+        }
+        SpaceAfter(sub_entry, spaces) => {
+            fmt_platform_rigid(buf, sub_entry, indent);
+            fmt_spaces(buf, spaces.iter(), indent);
+        }
+    }
 }
 
 fn fmt_imports<'a>(
@@ -124,14 +272,14 @@ fn fmt_to<'a>(buf: &mut String<'a>, to: To<'a>, indent: u16) {
     }
 }
 
-fn fmt_exposes<'a>(
+fn fmt_exposes<'a, N: FormatName + 'a>(
     buf: &mut String<'a>,
-    loc_entries: &'a Collection<'a, Located<ExposesEntry<'a, &'a str>>>,
+    loc_entries: Collection<'_, Located<ExposesEntry<'_, N>>>,
     indent: u16,
 ) {
     fmt_collection(
         buf,
-        *loc_entries,
+        loc_entries,
         indent,
         CollectionConfig {
             begin: '[',
@@ -141,7 +289,7 @@ fn fmt_exposes<'a>(
     );
 }
 
-impl<'a> Formattable<'a> for ExposesEntry<'a, &'a str> {
+impl<'a, 'b, N: FormatName> Formattable<'a> for ExposesEntry<'b, N> {
     fn is_multiline(&self) -> bool {
         false
     }
@@ -151,11 +299,31 @@ impl<'a> Formattable<'a> for ExposesEntry<'a, &'a str> {
     }
 }
 
-fn fmt_exposes_entry<'a>(buf: &mut String<'a>, entry: &ExposesEntry<'a, &'a str>, indent: u16) {
+pub trait FormatName {
+    fn format<'a>(&self, buf: &mut String<'a>);
+}
+
+impl<'a> FormatName for &'a str {
+    fn format<'b>(&self, buf: &mut String<'b>) {
+        buf.push_str(self)
+    }
+}
+
+impl<'a> FormatName for ModuleName<'a> {
+    fn format<'b>(&self, buf: &mut String<'b>) {
+        buf.push_str(self.as_str());
+    }
+}
+
+fn fmt_exposes_entry<'a, 'b, N: FormatName>(
+    buf: &mut String<'a>,
+    entry: &ExposesEntry<'b, N>,
+    indent: u16,
+) {
     use roc_parse::header::ExposesEntry::*;
 
     match entry {
-        Exposed(ident) => buf.push_str(ident),
+        Exposed(ident) => ident.format(buf),
 
         SpaceBefore(sub_entry, spaces) => {
             fmt_spaces(buf, spaces.iter(), indent);
@@ -260,8 +428,25 @@ fn fmt_imports_entry<'a>(buf: &mut String<'a>, entry: &ImportsEntry<'a>, indent:
             }
         }
 
-        Package(_pkg, _name, _entries) => {
-            todo!("TODO Format imported package");
+        Package(pkg, name, entries) => {
+            buf.push_str(pkg);
+            buf.push('.');
+            buf.push_str(name.as_str());
+
+            if !entries.is_empty() {
+                buf.push('.');
+
+                fmt_collection(
+                    buf,
+                    *entries,
+                    indent,
+                    CollectionConfig {
+                        begin: '{',
+                        end: '}',
+                        delimiter: ',',
+                    },
+                );
+            }
         }
 
         SpaceBefore(sub_entry, spaces) => {
diff --git a/compiler/fmt/src/spaces.rs b/compiler/fmt/src/spaces.rs
index afb8bc52db..1103449590 100644
--- a/compiler/fmt/src/spaces.rs
+++ b/compiler/fmt/src/spaces.rs
@@ -29,9 +29,9 @@ pub fn fmt_default_spaces<'a>(
     }
 }
 
-pub fn fmt_spaces<'b, 'a: 'b, I>(buf: &mut String<'a>, spaces: I, indent: u16)
+pub fn fmt_spaces<'a, 'b, I>(buf: &mut String<'a>, spaces: I, indent: u16)
 where
-    I: Iterator<Item = &'b CommentOrNewline<'a>>,
+    I: Iterator<Item = &'b CommentOrNewline<'b>>,
 {
     use self::CommentOrNewline::*;
 
@@ -85,13 +85,13 @@ pub enum NewlineAt {
 /// The `new_line_at` argument describes how new lines should be inserted
 /// at the beginning or at the end of the block
 /// in the case of there is some comment in the `spaces` argument.
-pub fn fmt_comments_only<'a, I>(
+pub fn fmt_comments_only<'a, 'b, I>(
     buf: &mut String<'a>,
     spaces: I,
     new_line_at: NewlineAt,
     indent: u16,
 ) where
-    I: Iterator<Item = &'a CommentOrNewline<'a>>,
+    I: Iterator<Item = &'b CommentOrNewline<'b>>,
 {
     use self::CommentOrNewline::*;
     use NewlineAt::*;
@@ -122,7 +122,7 @@ pub fn fmt_comments_only<'a, I>(
     }
 }
 
-fn fmt_comment<'a>(buf: &mut String<'a>, comment: &'a str) {
+fn fmt_comment<'a>(buf: &mut String<'a>, comment: &str) {
     buf.push('#');
     if !comment.starts_with(' ') {
         buf.push(' ');
@@ -130,7 +130,7 @@ fn fmt_comment<'a>(buf: &mut String<'a>, comment: &'a str) {
     buf.push_str(comment);
 }
 
-fn fmt_docs<'a>(buf: &mut String<'a>, docs: &'a str) {
+fn fmt_docs<'a>(buf: &mut String<'a>, docs: &str) {
     buf.push_str("##");
     if !docs.starts_with(' ') {
         buf.push(' ');
diff --git a/compiler/fmt/tests/test_fmt.rs b/compiler/fmt/tests/test_fmt.rs
index 689784559b..6442748d5b 100644
--- a/compiler/fmt/tests/test_fmt.rs
+++ b/compiler/fmt/tests/test_fmt.rs
@@ -2489,6 +2489,30 @@ mod test_fmt {
         ));
     }
 
+    #[test]
+    fn single_line_platform() {
+        // There are many places that there should probably be spaces, e.g.:
+        // requires { model=>Model, msg=>Msg } { main : Effect {} }
+        //                                             ^
+        // putLine : Str -> Effect {},
+        //          ^
+        // TODO: improve spacing
+        module_formats_same(
+            "platform folkertdev/foo \
+            requires { model=>Model, msg=>Msg } { main :Effect {} } \
+            exposes [] \
+            packages {} \
+            imports [ Task.{ Task } ] \
+            provides [ mainForHost ] \
+            effects fx.Effect \
+            { \
+                putLine :Str -> Effect {}, \
+                putInt :I64 -> Effect {}, \
+                getInt :Effect { value : I64, errorCode : [ A, B ], isError : Bool } \
+            } ",
+        );
+    }
+
     /// Annotations and aliases
 
     #[test]
diff --git a/compiler/load/src/file.rs b/compiler/load/src/file.rs
index d0a79e8169..4ac1f371e1 100644
--- a/compiler/load/src/file.rs
+++ b/compiler/load/src/file.rs
@@ -3437,7 +3437,7 @@ fn fabricate_effects_module<'a>(
 
     let module_id: ModuleId;
 
-    let effect_entries = unpack_exposes_entries(arena, effects.entries);
+    let effect_entries = unpack_exposes_entries(arena, effects.entries.items);
     let name = effects.effect_type_name;
     let declared_name: ModuleName = name.into();
 
diff --git a/compiler/parse/src/header.rs b/compiler/parse/src/header.rs
index 404e0cc601..abcf0aafd8 100644
--- a/compiler/parse/src/header.rs
+++ b/compiler/parse/src/header.rs
@@ -174,7 +174,7 @@ pub struct Effects<'a> {
     pub spaces_after_type_name: &'a [CommentOrNewline<'a>],
     pub effect_shortname: &'a str,
     pub effect_type_name: &'a str,
-    pub entries: &'a [Loc<TypedIdent<'a>>],
+    pub entries: Collection<'a, Loc<TypedIdent<'a>>>,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq)]
diff --git a/compiler/parse/src/module.rs b/compiler/parse/src/module.rs
index f0d2200e49..256a3c18e6 100644
--- a/compiler/parse/src/module.rs
+++ b/compiler/parse/src/module.rs
@@ -718,7 +718,7 @@ fn effects<'a>() -> impl Parser<'a, Effects<'a>, EEffects<'a>> {
                 spaces_after_type_name,
                 effect_shortname: type_shortname,
                 effect_type_name: type_name,
-                entries: entries.items,
+                entries,
             },
             state,
         ))