Initial commit

2023-02-26 22:48:34 +02:00 · 2023-02-26 22:48:34 +02:00 · c2117bc6ff
commit c2117bc6ff
19 changed files with 1926 additions and 0 deletions
--- a/.gitignore
+++ b/.gitignore
@ -0,0 +1,4 @@
+*.beam
+*.ez
+build
+erl_crash.dump
--- a/.tool-versions
+++ b/.tool-versions
@ -0,0 +1,2 @@
+erlang 25.2.2
+gleam 0.26.2
--- a/4
+++ b/4
@ -0,0 +1,4 @@
+1.0.0
+-----
+
+Initial release.
--- a/19
+++ b/19
@ -0,0 +1,19 @@
+Copyright (c) 2023 Mikko Ahlroth
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
--- a/README.md
+++ b/README.md
@ -0,0 +1,61 @@
+# glemplate
+
+[![Package Version](https://img.shields.io/hexpm/v/glemplate)](https://hex.pm/packages/glemplate)
+[![Hex Docs](https://img.shields.io/badge/hex-docs-ffaff3)](https://hexdocs.pm/glemplate/)
+
+Glemplate is a simplistic template engine for Gleam. The aim was to learn how to make such a thing
+and fill simple use cases. At this stage, it can be used for simple plain text and HTML templates,
+and for other contexts by supplying a custom encoding function.
+
+## Quick start
+
+```gleam
+import gleam/map
+import glemplate/parser
+import glemplate/html
+import glemplate/assigns
+
+let template = "<b>Welcome, <%= name %>!</b>"
+
+assert Ok(tpl) = parser.parse_to_template(template, "input.html.glemp")
+let assigns = assigns.from_list([#("name", assigns.String("<Nicd>"))])
+let template_cache = map.new()
+html.render(tpl, assigns, template_cache) // "<b>Welcome, &lt;Nicd&gt;!</b>"
+```
+
+The main modules:
+
+- [glemplate/parser](glemplate/parser.html): The parser implements and documents the string
+  template syntax.
+- [glemplate/ast](glemplate/ast.html): The abstract syntax tree (AST) is the data format of the
+  parsed templates.
+- [glemplate/renderer](glemplate/renderer.html): The renderer takes in the parsed AST, input data,
+  and a cache of templates, and renders the template into an output string builder.
+- [glemplate/html](glemplate/html.html) and [glemplate/text](glemplate/text.html) have helper
+  functions for rendering HTML and plain text templates.
+
+Using templates with Glemplate has two main things to deal with:
+
+1. parsing templates into AST with the parser, and
+2. rendering that AST into some output with assigns (input data).
+
+Since Gleam has no metaprogramming, the parsing of templates needs to be done at startup time (or
+whenever deemed necessary when templates have changed). The resulting AST should be stored for
+later use in e.g. ETS, process state, persistent_term…
+
+## Limitations
+
+- Static values in templates in place of variables aren't supported.
+- It's possible to create infinite loops with child templates, it's not recommended to give access
+  to writing templates to untrusted users.
+- Calling functions from templates is not supported.
+
+## Installation
+
+This package can be added to your Gleam project:
+
+```sh
+gleam add glemplate
+```
+
+and its documentation can be found at <https://hexdocs.pm/glemplate>.
--- a/gleam.toml
+++ b/gleam.toml
@ -0,0 +1,18 @@
+name = "glemplate"
+version = "1.0.0"
+description = "A Gleam project"
+
+# Fill out these fields if you intend to generate HTML documentation or publish
+# your project to the Hex package manager.
+#
+licences = ["MIT"]
+repository = { type = "gitlab", user = "Nicd", repo = "glemplate" }
+links = []
+
+[dependencies]
+gleam_stdlib = "~> 0.26"
+nibble = "~> 0.2"
+glentities = "~> 1.0"
+
+[dev-dependencies]
+gleeunit = "~> 0.10"
--- a/manifest.toml
+++ b/manifest.toml
@ -0,0 +1,15 @@
+# This file was generated by Gleam
+# You typically do not need to edit this file
+
+packages = [
+  { name = "gleam_stdlib", version = "0.26.1", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "B17BBE8A78F3909D93BCC6C24F531673A7E328A61F24222EB1E58D0A7552B1FE" },
+  { name = "gleeunit", version = "0.10.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "ECEA2DE4BE6528D36AFE74F42A21CDF99966EC36D7F25DEB34D47DD0F7977BAF" },
+  { name = "glentities", version = "1.0.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "glentities", source = "hex", outer_checksum = "9F602AB9A9DB0B4905BCDEC05B8586A77C17021210B85034AE3D182BD8024FE2" },
+  { name = "nibble", version = "0.2.2", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "nibble", source = "hex", outer_checksum = "B5D0E11DADEB4EC2F4ACD04DEB3CEBE3F0762B0BD9FF37805948FFC17017F791" },
+]
+
+[requirements]
+gleam_stdlib = "~> 0.26"
+gleeunit = "~> 0.10"
+glentities = "~> 1.0"
+nibble = "~> 0.2"
--- a/src/glemplate/assigns.gleam
+++ b/src/glemplate/assigns.gleam
@ -0,0 +1,59 @@
+//// Assigns are used to insert dynamic data into a template. This module
+//// contains convenience functions for creating assigns, but you may also
+//// create the map manually with Gleam's map functions if you so wish.
+
+import gleam/map.{Map}
+import glemplate/ast.{VarName}
+
+/// Data in an assign. Note that only `String` and `Int` are stringifiable
+/// values.
+pub type AssignData {
+  String(String)
+  Int(Int)
+
+  /// A function to execute that returns assign data on demand.
+  Lazy(LazyFn)
+  Bool(Bool)
+  Map(Map(VarName, AssignData))
+  List(List(AssignData))
+}
+
+/// Lazy function that should return assign data when executed.
+pub type LazyFn =
+  fn() -> AssignData
+
+/// Assigns given to a template for rendering dynamic content.
+pub type Assigns =
+  Map(VarName, AssignData)
+
+pub fn new() -> Assigns {
+  map.new()
+}
+
+pub fn from_list(list: List(#(VarName, AssignData))) -> Assigns {
+  map.from_list(list)
+}
+
+pub fn add_string(assigns: Assigns, name: VarName, value: String) {
+  map.insert(assigns, name, String(value))
+}
+
+pub fn add_int(assigns: Assigns, name: VarName, value: Int) {
+  map.insert(assigns, name, Int(value))
+}
+
+pub fn add_lazy(assigns: Assigns, name: VarName, value: LazyFn) {
+  map.insert(assigns, name, Lazy(value))
+}
+
+pub fn add_bool(assigns: Assigns, name: VarName, value: Bool) {
+  map.insert(assigns, name, Bool(value))
+}
+
+pub fn add_list(assigns: Assigns, name: VarName, value: List(AssignData)) {
+  map.insert(assigns, name, List(value))
+}
+
+pub fn add_map(assigns: Assigns, name: VarName, value: Map(VarName, AssignData)) {
+  map.insert(assigns, name, Map(value))
+}
--- a/src/glemplate/ast.gleam
+++ b/src/glemplate/ast.gleam
@ -0,0 +1,55 @@
+//// The abstract syntax tree that templates are stored as in memory. This AST
+//// can be rendered with the renderer module.
+
+pub type Node {
+  Text(String)
+  Dynamic(DynamicNode)
+  Nodes(nodes: NodeList)
+}
+
+pub type NodeList =
+  List(Node)
+
+pub type Template {
+  Template(name: TemplateName, nodes: NodeList)
+}
+
+/// A dynamic node is used for dynamic behaviour in a template.
+pub type DynamicNode {
+  /// Output the variable, encoded.
+  Output(Var)
+
+  /// Output the variable, without encoding.
+  RawOutput(Var)
+
+  /// Render a node list based on if the assign is truthy (non-false).
+  If(Var, if_true: NodeList, if_false: NodeList)
+
+  /// Iterate over the variable, bind it to a new name, and render the node list
+  /// for every item.
+  Iter(over: Var, binding: VarName, NodeList)
+
+  /// Render the given template, using the assigns mapping. The assigns mapping
+  /// is a list of tuples `(from, to)`, where the `from` named assigns are
+  /// available with `to` names in the child template.
+  Render(tpl: TemplateName, assigns_map: List(#(Var, VarName)))
+}
+
+/// A reference to a template with the given name.
+pub type TemplateName =
+  String
+
+/// A reference to a variable input.
+pub type Var {
+  /// Reference to an assign with the given name.
+  Assign(name: VarName)
+
+  /// Accessing a field of an associative container.
+  FieldAccess(container: Var, field: String)
+
+  /// Accessing an item in an indexable container.
+  IndexAccess(container: Var, index: Int)
+}
+
+pub type VarName =
+  String
--- a/src/glemplate/html.gleam
+++ b/src/glemplate/html.gleam
@ -0,0 +1,26 @@
+//// Utilities for rendering HTML templates.
+
+import gleam/string_builder.{StringBuilder}
+import glentities
+import glemplate/renderer
+import glemplate/ast
+import glemplate/assigns
+
+/// Encode content as HTML entities so it's safe in an HTML template.
+pub fn encode(text: String) -> StringBuilder {
+  glentities.encode(text, glentities.Named)
+  |> string_builder.from_string()
+}
+
+/// Render an HTML template.
+pub fn render(
+  template: ast.Template,
+  assigns: assigns.Assigns,
+  template_cache: renderer.TemplateCache,
+) -> renderer.RenderResult {
+  renderer.render(
+    template,
+    assigns,
+    renderer.RenderOptions(encoder: encode, template_cache: template_cache),
+  )
+}
--- a/src/glemplate/parser.gleam
+++ b/src/glemplate/parser.gleam
@ -0,0 +1,486 @@
+//// The parser transforms a string input into a template AST.
+////
+//// ## Template language description
+////
+//// The template language uses `<%` and `%>` as the tag delimiters. For
+//// outputting, the start delimiter `<%=` is used.
+////
+//// Comments can be inserted with `<%!-- Comment --%>`, they are not emitted to
+//// the AST.
+////
+//// Assigns can be referenced using their name (key in the assigns map). After
+//// an assign name, the contents of the assign can be accessed using field or
+//// index based access:
+////
+//// * `foo.bar` accesses field `bar` in assign `foo`.
+//// * `foo.0` accesses the first element in assign `foo`.
+////
+//// The accesses can be chained, e.g. `foo.bar.0.baz`. These access methods
+//// work in any place where an assign reference is expected.
+////
+//// Any other content in the template is emitted as text nodes.
+////
+//// ### Tags
+////
+//// #### Output
+////
+//// ```text
+//// <%= foo %>
+//// ```
+////
+//// Emits an output node of the assign `foo`. The contents are encoded using
+//// the encoder given in the render call.
+////
+//// #### Raw output
+////
+//// ```text
+//// <%= raw foo %>
+//// ```
+////
+//// Emits an output node of the assign `foo`. The contents are not encoded.
+////
+//// #### If
+////
+//// ```text
+//// <% if foo %>
+////   ...
+//// <% else %>
+////   ...
+//// <% end %>
+//// ```
+////
+//// Emits an if node. If the assign `foo` is truthy (not `False`), the first
+//// nodes are rendered, otherwise the nodes in the `else` block. The `else`
+//// block is optional.
+////
+//// #### For
+////
+//// ```text
+//// <% for bar in foo %>
+////   ...
+//// <% end %>
+//// ```
+////
+//// Emits a for node. Each item of `foo` is looped through, making it available
+//// as the assign `bar` inside the block. The contents of the block are
+//// rendered for each item.
+////
+//// #### Render
+////
+//// ```text
+//// <% render tpl.txt.glemp %>
+//// <% render tpl.txt.glemp name: user.name, level: user.level %>
+//// ```
+////
+//// Emits a render node. This will render another template in this place. The
+//// listed assigns will be the assigns given to the template. The name of the
+//// assign in the child template is on the left, the value is on the right.
+
+import gleam/string_builder
+import gleam/list
+import gleam/option.{None, Option, Some}
+import gleam/result
+import gleam/int
+import nibble
+import nibble/predicates
+import glemplate/ast
+
+const tag_start = "<%"
+
+const tag_end = "%>"
+
+const tag_escape_char = "%"
+
+const tag_comment_start = "!--"
+
+const tag_comment_end = "--"
+
+const tag_output = "="
+
+const end_token = "end"
+
+const if_token = "if"
+
+const else_token = "else"
+
+const iter_token = "for"
+
+const iter_oper_token = "in"
+
+const output_raw_token = "raw"
+
+const render_token = "render"
+
+const render_binding_separator = ":"
+
+const render_pair_separator = ","
+
+const access_separator = "."
+
+type IncompleteTag {
+  If(var: ast.Var, if_true: Option(ast.NodeList))
+  Iter(over: ast.Var, binding: ast.VarName)
+}
+
+type IncompleteAccess {
+  FieldAccess(field: String)
+  IndexAccess(index: Int)
+}
+
+type State {
+  State(
+    emitted: ast.NodeList,
+    current_text: string_builder.StringBuilder,
+    current_nodes: ast.NodeList,
+    current_tag: Option(IncompleteTag),
+    outer_state: Option(State),
+  )
+}
+
+/// Parse the string into a template with the given name.
+pub fn parse_to_template(template: String, name: String) {
+  try parsed = parse(template)
+
+  Ok(ast.Template(name: name, nodes: parsed))
+}
+
+/// Parse the string into a node list.
+pub fn parse(template: String) {
+  nibble.run(template, base_parser(empty_state()))
+  |> result.map(fn(state: State) { state.emitted })
+}
+
+fn empty_state() {
+  State(
+    emitted: [],
+    current_nodes: [],
+    current_text: string_builder.new(),
+    current_tag: None,
+    outer_state: None,
+  )
+}
+
+fn base_parser(old_state: State) {
+  nibble.loop(
+    old_state,
+    fn(state) {
+      nibble.one_of([
+        tag_parser(state)
+        |> nibble.map(nibble.Continue),
+        nibble.any()
+        |> nibble.map(fn(c) {
+          State(
+            ..state,
+            current_text: string_builder.append(state.current_text, c),
+          )
+        })
+        |> nibble.map(nibble.Continue),
+        nibble.eof()
+        |> nibble.replace(stringify_current_text(state))
+        |> nibble.map(nibble.Break),
+      ])
+    },
+  )
+  |> nibble.map(fn(state) {
+    State(
+      ..state,
+      emitted: [ast.Nodes(state.emitted), ..list.reverse(state.current_nodes)],
+      current_nodes: [],
+      current_text: string_builder.new(),
+    )
+  })
+}
+
+fn tag_parser(state: State) {
+  use _ <- nibble.then(nibble.string(tag_start))
+  let state = stringify_current_text(state)
+
+  nibble.one_of([
+    escaped_tag(state),
+    comment_tag(state),
+    output_tag(state),
+    other_tag(state),
+  ])
+}
+
+fn escaped_tag(state: State) {
+  nibble.string(tag_escape_char)
+  |> nibble.replace(
+    State(..state, current_nodes: [ast.Text(tag_start), ..state.current_nodes]),
+  )
+}
+
+fn comment_tag(state: State) {
+  use _ <- nibble.then(nibble.string(tag_comment_start))
+
+  nibble.loop(
+    Nil,
+    fn(_) {
+      nibble.one_of([
+        nibble.string(tag_comment_end <> tag_end)
+        |> nibble.map(nibble.Break),
+        nibble.any()
+        |> nibble.replace(nibble.Continue(Nil)),
+      ])
+    },
+  )
+  |> nibble.replace(state)
+}
+
+fn output_tag(state: State) {
+  use _ <- nibble.then(nibble.string(tag_output))
+
+  nibble.one_of([
+    {
+      // Raw output
+      use _ <- nibble.then(nibble.whitespace())
+      use _ <- nibble.then(nibble.string(output_raw_token))
+      use _ <- nibble.then(nibble.whitespace())
+      use var <- nibble.then(variable())
+
+      nibble.succeed(
+        State(
+          ..state,
+          current_nodes: [
+            ast.Dynamic(ast.RawOutput(var)),
+            ..state.current_nodes
+          ],
+        ),
+      )
+    },
+    {
+      // Normal output
+      use _ <- nibble.then(nibble.whitespace())
+      use var <- nibble.then(variable())
+
+      nibble.succeed(
+        State(
+          ..state,
+          current_nodes: [ast.Dynamic(ast.Output(var)), ..state.current_nodes],
+        ),
+      )
+    },
+  ])
+  |> nibble.drop(nibble.whitespace())
+  |> nibble.drop(nibble.string(tag_end))
+}
+
+fn other_tag(state: State) {
+  use _ <- nibble.then(nibble.whitespace())
+
+  nibble.one_of([
+    if_tag(state),
+    for_tag(state),
+    render_tag(state),
+    else_tag(state),
+    end_tag(state),
+  ])
+  |> nibble.drop(nibble.whitespace())
+  |> nibble.drop(nibble.string(tag_end))
+}
+
+fn if_tag(state: State) {
+  use _ <- nibble.then(nibble.string(if_token))
+  use _ <- nibble.then(nibble.whitespace())
+  use var <- nibble.then(variable())
+
+  nibble.succeed(
+    State(
+      ..empty_state(),
+      current_tag: Some(If(var, None)),
+      outer_state: Some(state),
+    ),
+  )
+}
+
+fn for_tag(state: State) {
+  use _ <- nibble.then(nibble.string(iter_token))
+  use _ <- nibble.then(nibble.whitespace())
+  use binding <- nibble.then(variable_name())
+  use _ <- nibble.then(nibble.whitespace())
+  use _ <- nibble.then(nibble.string(iter_oper_token))
+  use _ <- nibble.then(nibble.whitespace())
+  use over <- nibble.then(variable())
+
+  nibble.succeed(
+    State(
+      ..empty_state(),
+      current_tag: Some(Iter(over, binding)),
+      outer_state: Some(state),
+    ),
+  )
+}
+
+fn render_tag(state: State) {
+  use _ <- nibble.then(nibble.string(render_token))
+  use _ <- nibble.then(nibble.whitespace())
+  use filename <- nibble.then(filename())
+  use _ <- nibble.then(nibble.whitespace())
+
+  nibble.many(render_binding(), render_separator())
+  |> nibble.map(fn(bindings) {
+    State(
+      ..state,
+      current_nodes: [
+        ast.Dynamic(ast.Render(filename, bindings)),
+        ..state.current_nodes
+      ],
+    )
+  })
+}
+
+fn end_tag(state: State) {
+  use _ <- nibble.then(nibble.string(end_token))
+
+  let outer_state =
+    option.lazy_unwrap(state.outer_state, fn() { empty_state() })
+
+  case state.current_tag {
+    Some(If(var, if_true)) -> {
+      let #(if_true, state) = case if_true {
+        Some(if_true_nodes) -> #(if_true_nodes, state)
+        None -> #(
+          list.reverse(state.current_nodes),
+          State(..state, current_nodes: []),
+        )
+      }
+      let if_false = list.reverse(state.current_nodes)
+      nibble.succeed(
+        State(
+          ..outer_state,
+          current_nodes: [
+            ast.Dynamic(ast.If(var, if_true, if_false)),
+            ..outer_state.current_nodes
+          ],
+        ),
+      )
+    }
+
+    Some(Iter(over, binding)) ->
+      nibble.succeed(
+        State(
+          ..outer_state,
+          current_nodes: [
+            ast.Dynamic(ast.Iter(
+              over,
+              binding,
+              list.reverse(state.current_nodes),
+            )),
+            ..outer_state.current_nodes
+          ],
+        ),
+      )
+    _else -> nibble.fail("Expected `if` or `for` tag for `end` tag")
+  }
+}
+
+fn else_tag(state: State) {
+  use _ <- nibble.then(nibble.string(else_token))
+
+  case state.current_tag {
+    Some(If(var, None)) ->
+      nibble.succeed(
+        State(
+          ..state,
+          current_tag: Some(If(var, Some(list.reverse(state.current_nodes)))),
+          current_nodes: [],
+        ),
+      )
+
+    _else -> nibble.fail("Expected `if` to match `else` tag")
+  }
+}
+
+fn stringify_current_text(state: State) {
+  State(
+    ..state,
+    current_nodes: [
+      ast.Text(string_builder.to_string(state.current_text)),
+      ..state.current_nodes
+    ],
+    current_text: string_builder.new(),
+  )
+}
+
+fn variable_name() {
+  nibble.take_if_and_while(
+    fn(grapheme) { predicates.is_alphanum(grapheme) || grapheme == "_" },
+    "a variable name",
+  )
+}
+
+fn field_access() {
+  nibble.take_if_and_while(
+    fn(grapheme) { predicates.is_alphanum(grapheme) || grapheme == "_" },
+    "a field accessor",
+  )
+}
+
+fn index_access() {
+  nibble.take_if_and_while(predicates.is_digit, "an index accessor")
+}
+
+fn accessors() {
+  use accessors <- nibble.map(nibble.many(
+    nibble.one_of([field_access(), index_access()]),
+    nibble.string(access_separator),
+  ))
+
+  list.map(
+    accessors,
+    fn(accessor) {
+      case int.parse(accessor) {
+        Ok(data) -> IndexAccess(data)
+        Error(_) -> FieldAccess(accessor)
+      }
+    },
+  )
+}
+
+fn variable() {
+  use name <- nibble.then(variable_name())
+  use accessors <- nibble.then(nibble.one_of([
+    {
+      use _ <- nibble.then(nibble.string(access_separator))
+      use accs <- nibble.then(accessors())
+      nibble.succeed(accs)
+    },
+    nibble.succeed([]),
+  ]))
+
+  nibble.succeed(list.fold(
+    accessors,
+    ast.Assign(name),
+    fn(acc, accessor) {
+      case accessor {
+        FieldAccess(field) -> ast.FieldAccess(acc, field)
+        IndexAccess(index) -> ast.IndexAccess(acc, index)
+      }
+    },
+  ))
+}
+
+fn filename() {
+  nibble.take_if_and_while(
+    fn(grapheme) {
+      predicates.is_alphanum(grapheme) || grapheme == "_" || grapheme == "-" || grapheme == "."
+    },
+    "a filename without spaces",
+  )
+}
+
+fn render_binding() {
+  use to <- nibble.then(variable_name())
+  use _ <- nibble.then(nibble.string(render_binding_separator))
+  use _ <- nibble.then(nibble.whitespace())
+  use from <- nibble.then(variable())
+
+  nibble.succeed(#(from, to))
+}
+
+fn render_separator() {
+  use _ <- nibble.then(nibble.string(render_pair_separator))
+  use _ <- nibble.then(nibble.whitespace())
+
+  nibble.succeed(Nil)
+}
--- a/src/glemplate/renderer.gleam
+++ b/src/glemplate/renderer.gleam
@ -0,0 +1,294 @@
+//// The renderer is given the template AST and some assigns, which it will
+//// render into a string output.
+
+import gleam/map.{Map}
+import gleam/int
+import gleam/string_builder.{StringBuilder}
+import gleam/result
+import gleam/list
+import glemplate/assigns.{AssignData, Assigns}
+import glemplate/result as result_helpers
+import glemplate/ast
+
+pub type RenderError {
+  /// A referenced assign was not found.
+  AssignNotFound(assign: ast.Var, assigns: Assigns)
+
+  /// A referenced assign was not iterable.
+  AssignNotIterable(assign: ast.Var, assigns: Assigns)
+
+  /// A referenced assign could not be stringified.
+  AssignNotStringifiable(assign: ast.Var, assigns: Assigns)
+
+  AssignFieldNotFound(assign: ast.Var, field: String, assigns: Assigns)
+
+  AssignNotFieldAccessible(assign: ast.Var, assigns: Assigns)
+
+  AssignIndexOutOfBounds(assign: ast.Var, index: Int, assigns: Assigns)
+
+  AssignNotIndexable(assign: ast.Var, assigns: Assigns)
+
+  /// A referenced child template was not found in the template cache.
+  ChildTemplateNotFound(tpl_name: ast.TemplateName)
+}
+
+pub type StringifyError {
+  StringifyError
+}
+
+type AssignResult =
+  Result(AssignData, RenderError)
+
+pub type RenderResult =
+  Result(StringBuilder, RenderError)
+
+/// Function to encode potentially dangerous contents into the template in a
+/// safe way. E.g. encode text with HTML entities in an HTML template.
+pub type EncoderFn =
+  fn(String) -> StringBuilder
+
+/// A cache of templates to use for rendering child templates.
+pub type TemplateCache =
+  Map(ast.TemplateName, ast.Template)
+
+pub type RenderOptions {
+  RenderOptions(encoder: EncoderFn, template_cache: TemplateCache)
+}
+
+/// Render given template with the assigns and options.
+pub fn render(
+  template: ast.Template,
+  assigns: Assigns,
+  opts: RenderOptions,
+) -> RenderResult {
+  render_nodes(template.nodes, assigns, string_builder.new(), opts)
+}
+
+fn render_nodes(
+  nodes: ast.NodeList,
+  assigns: Assigns,
+  acc: StringBuilder,
+  options: RenderOptions,
+) -> RenderResult {
+  result_helpers.fold(
+    nodes,
+    acc,
+    fn(acc, node) { render_node(node, assigns, acc, options) },
+  )
+}
+
+fn render_node(
+  node: ast.Node,
+  assigns: Assigns,
+  acc: StringBuilder,
+  options: RenderOptions,
+) -> RenderResult {
+  case node {
+    ast.Text(str) -> Ok(string_builder.append(acc, str))
+    ast.Dynamic(dynamic) -> render_dynamic(dynamic, assigns, acc, options)
+    ast.Nodes(nodes) -> render_nodes(nodes, assigns, acc, options)
+  }
+}
+
+fn render_dynamic(
+  node: ast.DynamicNode,
+  assigns: Assigns,
+  acc: StringBuilder,
+  options: RenderOptions,
+) -> RenderResult {
+  case node {
+    ast.Output(var) ->
+      get_assign(assigns, var)
+      |> result.then(fn(data) {
+        render_output(data, False, var, assigns, acc, options)
+      })
+    ast.RawOutput(var) ->
+      get_assign(assigns, var)
+      |> result.then(fn(data) {
+        render_output(data, True, var, assigns, acc, options)
+      })
+    ast.If(var, if_true, if_false) ->
+      get_assign(assigns, var)
+      |> result.then(fn(data) {
+        render_if(data, if_true, if_false, assigns, acc, options)
+      })
+    ast.Iter(over, binding, nodes) ->
+      get_assign(assigns, over)
+      |> result.then(fn(data) {
+        render_iter(data, over, binding, nodes, assigns, acc, options)
+      })
+    ast.Render(tpl, assigns_map) ->
+      render_child(tpl, assigns, assigns_map, acc, options)
+  }
+}
+
+fn render_output(
+  data: AssignData,
+  raw: Bool,
+  var: ast.Var,
+  assigns: Assigns,
+  acc: StringBuilder,
+  options: RenderOptions,
+) -> RenderResult {
+  let str_result = stringify(data)
+
+  case str_result {
+    Ok(str) -> {
+      let out = case raw {
+        True -> string_builder.append(acc, str)
+        False -> string_builder.append_builder(acc, options.encoder(str))
+      }
+      Ok(out)
+    }
+
+    Error(_) -> Error(AssignNotStringifiable(assign: var, assigns: assigns))
+  }
+}
+
+fn render_if(
+  data: AssignData,
+  if_true: ast.NodeList,
+  if_false: ast.NodeList,
+  assigns: Assigns,
+  acc: StringBuilder,
+  options: RenderOptions,
+) -> RenderResult {
+  case data {
+    assigns.Bool(False) -> render_nodes(if_false, assigns, acc, options)
+    _truthy -> render_nodes(if_true, assigns, acc, options)
+  }
+}
+
+fn render_iter(
+  data: AssignData,
+  over: ast.Var,
+  binding: ast.VarName,
+  nodes: ast.NodeList,
+  assigns: Assigns,
+  acc: StringBuilder,
+  options: RenderOptions,
+) -> RenderResult {
+  case data {
+    assigns.List(items) ->
+      result_helpers.fold(
+        items,
+        acc,
+        fn(output, item) {
+          let new_assigns = map.insert(assigns, binding, item)
+          render_nodes(nodes, new_assigns, output, options)
+        },
+      )
+
+    _other -> Error(AssignNotIterable(assign: over, assigns: assigns))
+  }
+}
+
+fn render_child(
+  template_name: ast.TemplateName,
+  assigns: Assigns,
+  assigns_map: List(#(ast.Var, ast.VarName)),
+  acc: StringBuilder,
+  options: RenderOptions,
+) -> RenderResult {
+  try template =
+    map.get(options.template_cache, template_name)
+    |> result.replace_error(ChildTemplateNotFound(tpl_name: template_name))
+
+  try new_assigns =
+    result_helpers.fold(
+      assigns_map,
+      map.new(),
+      fn(acc, mapping) {
+        let #(from, to) = mapping
+        try assign = get_assign(assigns, from)
+        Ok(map.insert(acc, to, assign))
+      },
+    )
+
+  render_nodes(template.nodes, new_assigns, acc, options)
+}
+
+fn get_assign(assigns: Assigns, var: ast.Var) -> AssignResult {
+  try data = case var {
+    ast.Assign(name) -> {
+      let get_result = map.get(assigns, name)
+      case get_result {
+        Ok(data) -> Ok(data)
+        Error(_) -> Error(AssignNotFound(assign: var, assigns: assigns))
+      }
+    }
+
+    ast.FieldAccess(container, field) -> {
+      try data = get_assign(assigns, container)
+      access_field(data, field, var, assigns)
+    }
+
+    ast.IndexAccess(container, index) -> {
+      try data = get_assign(assigns, container)
+      access_index(data, index, var, assigns)
+    }
+  }
+
+  // In case the data is a lazy function, it must be resolved
+  Ok(resolve_lazy(data))
+}
+
+fn access_field(
+  container: AssignData,
+  field: String,
+  accessor: ast.Var,
+  assigns: Assigns,
+) -> AssignResult {
+  case container {
+    assigns.Map(map) ->
+      case map.get(map, field) {
+        Ok(data) -> Ok(data)
+        Error(_) ->
+          Error(AssignFieldNotFound(
+            assign: accessor,
+            field: field,
+            assigns: assigns,
+          ))
+      }
+
+    _other ->
+      Error(AssignNotFieldAccessible(assign: accessor, assigns: assigns))
+  }
+}
+
+fn access_index(
+  container: AssignData,
+  index: Int,
+  accessor: ast.Var,
+  assigns: Assigns,
+) -> AssignResult {
+  case container {
+    assigns.List(l) ->
+      case list.at(l, index) {
+        Ok(data) -> Ok(data)
+        Error(_) ->
+          Error(AssignIndexOutOfBounds(
+            assign: accessor,
+            index: index,
+            assigns: assigns,
+          ))
+      }
+
+    _other -> Error(AssignNotIndexable(assign: accessor, assigns: assigns))
+  }
+}
+
+fn stringify(data: AssignData) -> Result(String, StringifyError) {
+  case data {
+    assigns.String(s) -> Ok(s)
+    assigns.Int(i) -> Ok(int.to_string(i))
+    _other -> Error(StringifyError)
+  }
+}
+
+fn resolve_lazy(data: AssignData) -> AssignData {
+  case data {
+    assigns.Lazy(lazy_fn) -> resolve_lazy(lazy_fn())
+    other -> other
+  }
+}
--- a/src/glemplate/result.gleam
+++ b/src/glemplate/result.gleam
@ -0,0 +1,24 @@
+//// Helper utilities for result types.
+
+import gleam/list.{Continue, Stop}
+
+/// Fold over a list, stopping at the first error encountered.
+pub fn fold(
+  items: List(a),
+  init: b,
+  folder: fn(b, a) -> Result(b, c),
+) -> Result(b, c) {
+  list.fold_until(
+    items,
+    Ok(init),
+    fn(acc, item) {
+      assert Ok(acc) = acc
+      let res = folder(acc, item)
+
+      case res {
+        Ok(next_acc) -> Continue(Ok(next_acc))
+        Error(error) -> Stop(Error(error))
+      }
+    },
+  )
+}
--- a/src/glemplate/text.gleam
+++ b/src/glemplate/text.gleam
@ -0,0 +1,24 @@
+//// Utilities for rendering plain text templates.
+
+import gleam/string_builder
+import glemplate/renderer
+import glemplate/ast
+import glemplate/assigns
+
+/// An encoder that just returns the content as-is.
+pub fn encode(str: String) {
+  string_builder.from_string(str)
+}
+
+/// Render a plain text template.
+pub fn render(
+  template: ast.Template,
+  assigns: assigns.Assigns,
+  template_cache: renderer.TemplateCache,
+) -> renderer.RenderResult {
+  renderer.render(
+    template,
+    assigns,
+    renderer.RenderOptions(encoder: encode, template_cache: template_cache),
+  )
+}
--- a/test/glemplate_test.gleam
+++ b/test/glemplate_test.gleam
@ -0,0 +1,5 @@
+import gleeunit
+
+pub fn main() {
+  gleeunit.main()
+}
--- a/test/html_test.gleam
+++ b/test/html_test.gleam
@ -0,0 +1,24 @@
+import gleam/map
+import gleam/string_builder
+import gleeunit/should
+import glemplate/parser
+import glemplate/html
+import glemplate/assigns
+
+pub fn encoding_test() {
+  let template = "<b>Welcome, <%= name %>!</b> <%= raw name %>"
+
+  assert Ok(tpl) = parser.parse_to_template(template, "input.html.glemp")
+
+  let template_cache = map.new()
+  let assigns =
+    assigns.new()
+    |> assigns.add_string("name", "||<xXx_KillaBoy_69>||")
+
+  assert Ok(result) = html.render(tpl, assigns, template_cache)
+
+  should.equal(
+    string_builder.to_string(result),
+    "<b>Welcome, &vert;&vert;&lt;xXx&lowbar;KillaBoy&lowbar;69&gt;&vert;&vert;!</b> ||<xXx_KillaBoy_69>||",
+  )
+}
--- a/test/parser_test.gleam
+++ b/test/parser_test.gleam
@ -0,0 +1,362 @@
+import gleeunit/should
+import glemplate/parser
+import glemplate/ast.{
+  Assign, Dynamic, FieldAccess, If, IndexAccess, Iter, Nodes, Output, RawOutput,
+  Render, Text,
+}
+
+pub fn output_test() {
+  let template = "<%= aurora %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [Nodes([]), Text(""), Dynamic(Output(Assign("aurora"))), Text("")],
+  )
+}
+
+pub fn raw_output_test() {
+  let template = "<%= raw aurora %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [Nodes([]), Text(""), Dynamic(RawOutput(Assign("aurora"))), Text("")],
+  )
+}
+
+pub fn if_test() {
+  let template = "<% if martin %>Hello, I'm Martin<% end %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(If(Assign("martin"), [Text("Hello, I'm Martin")], [])),
+      Text(""),
+    ],
+  )
+}
+
+pub fn if_else_test() {
+  let template =
+    "<% if martin %>Hello, I'm Martin<% else %>Sorry, I think you've mistaken me for someone else<% end %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(If(
+        Assign("martin"),
+        [Text("Hello, I'm Martin")],
+        [Text("Sorry, I think you've mistaken me for someone else")],
+      )),
+      Text(""),
+    ],
+  )
+}
+
+pub fn for_test() {
+  let template = "<% for item in shopping %>- <%= item %><% end %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(Iter(
+        Assign("shopping"),
+        "item",
+        [Text("- "), Dynamic(Output(Assign("item"))), Text("")],
+      )),
+      Text(""),
+    ],
+  )
+}
+
+pub fn render_test() {
+  let template = "<% render foo %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [Nodes([]), Text(""), Dynamic(Render("foo", [])), Text("")],
+  )
+}
+
+pub fn render_1_binding_test() {
+  let template = "<% render foo a: b %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(Render("foo", [#(Assign("b"), "a")])),
+      Text(""),
+    ],
+  )
+}
+
+pub fn render_n_bindings_test() {
+  let template = "<% render foo a: b, c: d, e: f %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(Render(
+        "foo",
+        [#(Assign("b"), "a"), #(Assign("d"), "c"), #(Assign("f"), "e")],
+      )),
+      Text(""),
+    ],
+  )
+}
+
+pub fn field_access_test() {
+  let template = "<%= aurora.conqueror %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(Output(FieldAccess(Assign("aurora"), "conqueror"))),
+      Text(""),
+    ],
+  )
+}
+
+pub fn index_access_test() {
+  let template = "<%= aurora.0 %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(Output(IndexAccess(Assign("aurora"), 0))),
+      Text(""),
+    ],
+  )
+}
+
+pub fn chained_access_test() {
+  let template = "<%= aurora.albums.0.publish_year %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(Output(FieldAccess(
+        IndexAccess(FieldAccess(Assign("aurora"), "albums"), 0),
+        "publish_year",
+      ))),
+      Text(""),
+    ],
+  )
+}
+
+pub fn raw_field_access_test() {
+  let template = "<%= raw aurora.conqueror %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(RawOutput(FieldAccess(Assign("aurora"), "conqueror"))),
+      Text(""),
+    ],
+  )
+}
+
+pub fn if_field_access_test() {
+  let template = "<% if user.is_martin %>Hello, I'm Martin<% end %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(If(
+        FieldAccess(Assign("user"), "is_martin"),
+        [Text("Hello, I'm Martin")],
+        [],
+      )),
+      Text(""),
+    ],
+  )
+}
+
+pub fn for_access_test() {
+  let template = "<% for item in user.shopping_lists.0 %>- <%= item %><% end %>"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text(""),
+      Dynamic(Iter(
+        IndexAccess(FieldAccess(Assign("user"), "shopping_lists"), 0),
+        "item",
+        [Text("- "), Dynamic(Output(Assign("item"))), Text("")],
+      )),
+      Text(""),
+    ],
+  )
+}
+
+pub fn complex_test() {
+  let template =
+    "<h1>HIGH SCORES:</h1>
+<ul>
+  <% for score in scores %>
+    <li>
+      <% if score %>
+        <% render score_tpl.html.glemp score: score %>
+      <% end %>
+    </li>
+  <% end %>
+</ul>
+
+You can create comments by using comment tags: <%%!-- Comment --%>
+
+<%!-- The pyramid: --%>
+<% if user %>
+  <% if other_user %>
+    <% if third_user %>
+      <% for item in user.items %>
+        - User's item: <%= item %>
+        <% for ou_item in other_user.items %>
+          - Other user's item: <%= ou_item %>
+          <% for tu_item in third_user.items %>
+            - Third user's item: <%= tu_item %>
+
+            <% render item_combos.html.glemp item_1: item, item_2: ou_item, item_3: tu_item %>
+          <% end %>
+        <% end %>
+      <% end %>
+    <% else %>
+      Third user not found!
+    <% end %>
+  <% else %>
+    Second user not found!
+  <% end %>
+<% else %>
+  User not found!
+<% end %>
+"
+
+  assert Ok(parsed) = parser.parse(template)
+  should.equal(
+    parsed,
+    [
+      Nodes([]),
+      Text("<h1>HIGH SCORES:</h1>\n<ul>\n  "),
+      Dynamic(Iter(
+        Assign("scores"),
+        "score",
+        [
+          Text("\n    <li>\n      "),
+          Dynamic(If(
+            Assign("score"),
+            [
+              Text("\n        "),
+              Dynamic(Render(
+                "score_tpl.html.glemp",
+                [#(Assign("score"), "score")],
+              )),
+              Text("\n      "),
+            ],
+            [],
+          )),
+          Text("\n    </li>\n  "),
+        ],
+      )),
+      Text("\n</ul>\n\nYou can create comments by using comment tags: "),
+      Text("<%"),
+      Text("!-- Comment --%>\n\n"),
+      Text("\n"),
+      Dynamic(If(
+        Assign("user"),
+        [
+          Text("\n  "),
+          Dynamic(If(
+            Assign("other_user"),
+            [
+              Text("\n    "),
+              Dynamic(If(
+                Assign("third_user"),
+                [
+                  Text("\n      "),
+                  Dynamic(Iter(
+                    FieldAccess(Assign("user"), "items"),
+                    "item",
+                    [
+                      Text("\n        - User's item: "),
+                      Dynamic(Output(Assign("item"))),
+                      Text("\n        "),
+                      Dynamic(Iter(
+                        FieldAccess(Assign("other_user"), "items"),
+                        "ou_item",
+                        [
+                          Text("\n          - Other user's item: "),
+                          Dynamic(Output(Assign("ou_item"))),
+                          Text("\n          "),
+                          Dynamic(Iter(
+                            FieldAccess(Assign("third_user"), "items"),
+                            "tu_item",
+                            [
+                              Text("\n            - Third user's item: "),
+                              Dynamic(Output(Assign("tu_item"))),
+                              Text("\n\n            "),
+                              Dynamic(Render(
+                                "item_combos.html.glemp",
+                                [
+                                  #(Assign("item"), "item_1"),
+                                  #(Assign("ou_item"), "item_2"),
+                                  #(Assign("tu_item"), "item_3"),
+                                ],
+                              )),
+                              Text("\n          "),
+                            ],
+                          )),
+                          Text("\n        "),
+                        ],
+                      )),
+                      Text("\n      "),
+                    ],
+                  )),
+                  Text("\n    "),
+                ],
+                [Text("\n      Third user not found!\n    ")],
+              )),
+              Text("\n  "),
+            ],
+            [Text("\n    Second user not found!\n  ")],
+          )),
+          Text("\n"),
+        ],
+        [Text("\n  User not found!\n")],
+      )),
+      Text("\n"),
+    ],
+  )
+}
--- a/test/renderer_test.gleam
+++ b/test/renderer_test.gleam
@ -0,0 +1,420 @@
+import gleam/map
+import gleam/string_builder
+import gleeunit/should
+import glemplate/assigns.{Assigns, Bool, Int, Lazy, List, Map, String}
+import glemplate/ast.{
+  Assign, Dynamic, FieldAccess, If, IndexAccess, Iter, NodeList, Nodes, Output,
+  RawOutput, Render, Template, Text,
+}
+import glemplate/renderer
+
+pub fn empty_test() {
+  should.equal(render_to_string([], map.new()), "")
+}
+
+pub fn text_test() {
+  should.equal(
+    render_to_string([Text("foo"), Text(" bar "), Text("baz")], map.new()),
+    "foo bar baz",
+  )
+}
+
+pub fn nested_test() {
+  should.equal(
+    render_to_string(
+      [Nodes([Nodes([Text("foo")])]), Nodes([Nodes([Nodes([])])])],
+      map.new(),
+    ),
+    "foo",
+  )
+}
+
+pub fn var_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", String("bar"))
+  should.equal(
+    render_to_string(
+      [Text("<b>"), Dynamic(Output(Assign("foo"))), Text("</b>")],
+      assigns,
+    ),
+    "<b>bar</b>",
+  )
+}
+
+pub fn encoder_test() {
+  assert Ok(builder) =
+    renderer.render(
+      Template(
+        name: "TestTpl",
+        nodes: [
+          Dynamic(Output(Assign("foo"))),
+          Dynamic(RawOutput(Assign("foo"))),
+        ],
+      ),
+      map.new()
+      |> map.insert("foo", String("🙂")),
+      renderer.RenderOptions(
+        encoder: fn(_content) { string_builder.from_string("🙃") },
+        template_cache: map.new(),
+      ),
+    )
+  should.equal(string_builder.to_string(builder), "🙃🙂")
+}
+
+pub fn int_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", Int(1_000_000))
+  should.equal(
+    render_to_string([Dynamic(Output(Assign("foo")))], assigns),
+    "1000000",
+  )
+}
+
+pub fn lazy_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", Lazy(fn() { String("awesome") }))
+  should.equal(
+    render_to_string([Dynamic(Output(Assign("foo")))], assigns),
+    "awesome",
+  )
+}
+
+pub fn if_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", Bool(True))
+  should.equal(
+    render_to_string(
+      [Dynamic(If(Assign("foo"), [Text("yes")], [Text("no")]))],
+      assigns,
+    ),
+    "yes",
+  )
+}
+
+// Lazy function should not be called in code path that is not entered
+pub fn if_lazy_test() {
+  let assigns: Assigns =
+    map.from_list([
+      #("foo", Bool(True)),
+      #(
+        "lazy",
+        Lazy(fn() {
+          should.fail()
+          Bool(False)
+        }),
+      ),
+    ])
+  should.equal(
+    render_to_string(
+      [
+        Dynamic(If(
+          Assign("foo"),
+          [Text("yes")],
+          [Dynamic(Output(Assign("lazy")))],
+        )),
+      ],
+      assigns,
+    ),
+    "yes",
+  )
+}
+
+pub fn iter_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", List([String("first"), Int(2), String("third")]))
+  should.equal(
+    render_to_string(
+      [
+        Dynamic(Iter(
+          Assign("foo"),
+          "bar",
+          [Text("* "), Dynamic(Output(Assign("bar"))), Text("\n")],
+        )),
+      ],
+      assigns,
+    ),
+    "* first\n* 2\n* third\n",
+  )
+}
+
+pub fn render_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("parent_assign", Bool(False))
+  should.equal(
+    render_to_string(
+      [
+        Text("child tpl -- "),
+        Dynamic(Render("ChildTpl", [#(Assign("parent_assign"), "child_assign")])),
+        Text(" -- end child tpl"),
+      ],
+      assigns,
+    ),
+    "child tpl -- child_assign is false -- end child tpl",
+  )
+}
+
+pub fn field_access_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", Map(map.from_list([#("bar", String("baz"))])))
+  should.equal(
+    render_to_string(
+      [
+        Text("<b>"),
+        Dynamic(Output(FieldAccess(Assign("foo"), "bar"))),
+        Text("</b>"),
+      ],
+      assigns,
+    ),
+    "<b>baz</b>",
+  )
+}
+
+pub fn index_access_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", List([String("bar"), String("baz")]))
+  should.equal(
+    render_to_string(
+      [
+        Text("<b>"),
+        Dynamic(Output(IndexAccess(Assign("foo"), 1))),
+        Text("</b>"),
+      ],
+      assigns,
+    ),
+    "<b>baz</b>",
+  )
+}
+
+pub fn complex_test() {
+  let assigns: Assigns =
+    map.from_list([
+      #(
+        "user",
+        Map(map.from_list([
+          #("name", String("Nicd")),
+          #("registered", Lazy(fn() { String("2023-01-31") })),
+          #("points", Int(13_992_355_986)),
+          #("level", Int(32)),
+          #("paid", Bool(True)),
+          #(
+            "top_languages",
+            List([
+              String("Gleam"),
+              String("Elixir"),
+              String("TypeScript"),
+              String("JavaScript"),
+              String("Python"),
+              String("YaBasic"),
+              String("VHDL"),
+              String("GTLT"),
+            ]),
+          ),
+        ])),
+      ),
+    ])
+
+  let str =
+    render_to_string(
+      [
+        Text("User information:\n"),
+        Text("\n"),
+        Nodes([
+          Dynamic(Output(FieldAccess(Assign("user"), "name"))),
+          Text(" - "),
+          Dynamic(Render(
+            "points.txt.glemp",
+            assigns_map: [
+              #(FieldAccess(Assign("user"), "level"), "level"),
+              #(FieldAccess(Assign("user"), "points"), "points"),
+            ],
+          )),
+          Text("\n"),
+        ]),
+        Text("Registered on "),
+        Dynamic(Output(FieldAccess(Assign("user"), "registered"))),
+        Dynamic(If(
+          FieldAccess(Assign("user"), "paid"),
+          [Text(" (awesome supporter).")],
+          [Text(".")],
+        )),
+        Text("\n\n"),
+        Text("User's top languages\n"),
+        Text("--------------------\n"),
+        Dynamic(Iter(
+          FieldAccess(Assign("user"), "top_languages"),
+          "lang",
+          [Text("* "), Dynamic(Output(Assign("lang"))), Text("\n")],
+        )),
+      ],
+      assigns,
+    )
+
+  should.equal(
+    str,
+    "User information:
+
+Nicd - 13992355986 XP (level 32)
+Registered on 2023-01-31 (awesome supporter).
+
+User's top languages
+--------------------
+* Gleam
+* Elixir
+* TypeScript
+* JavaScript
+* Python
+* YaBasic
+* VHDL
+* GTLT
+",
+  )
+}
+
+pub fn hayleigh_test() {
+  let assigns: Assigns =
+    map.from_list([
+      #("my_var", String(":)")),
+      #("pekka", Bool(False)),
+      #("some_items", List([String("first"), Int(2), String("third")])),
+      #("user", String("Nicd")),
+    ])
+
+  let str =
+    render_to_string(
+      [
+        Text("<% <-- Escaped\n\n\n\nJotain tämmöstä <b>"),
+        Dynamic(Output(Assign("my_var"))),
+        Text("</b>.\nRaw variable: "),
+        Dynamic(RawOutput(Assign("my_var"))),
+        Text(".\n\n"),
+        Dynamic(If(
+          Assign("pekka"),
+          [Text("Olen pekka.\n")],
+          [Text("En ole pekka.\n")],
+        )),
+        Text("\n\n"),
+        Dynamic(Iter(
+          Assign("some_items"),
+          "item",
+          [Text(" * "), Dynamic(Output(Assign("item"))), Text("\n")],
+        )),
+        Text("\n\n\n"),
+        Dynamic(Render("some_template", [#(Assign("user"), "user")])),
+      ],
+      assigns,
+    )
+
+  should.equal(
+    str,
+    "<% <-- Escaped\n\n\n\nJotain tämmöstä <b>:)</b>.\nRaw variable: :).\n\nEn ole pekka.\n\n\n * first\n * 2\n * third\n\n\n\n",
+  )
+}
+
+pub fn unstringifiable_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", Bool(True))
+  should.be_error(render_tpl([Dynamic(Output(Assign("foo")))], assigns))
+}
+
+pub fn missing_assign_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo2", String("bar"))
+  should.be_error(render_tpl([Dynamic(Output(Assign("foo")))], assigns))
+}
+
+pub fn not_iterable_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", String("bar"))
+  should.be_error(render_tpl(
+    [Dynamic(Iter(Assign("foo"), "binding", []))],
+    assigns,
+  ))
+}
+
+pub fn missing_child_test() {
+  let assigns: Assigns = map.new()
+  should.be_error(render_tpl([Dynamic(Render("no", []))], assigns))
+}
+
+fn render_to_string(nodes: NodeList, assigns: Assigns) {
+  assert Ok(builder) = render_tpl(nodes, assigns)
+
+  string_builder.to_string(builder)
+}
+
+fn render_tpl(nodes: NodeList, assigns: Assigns) {
+  renderer.render(
+    Template(name: "TestTpl", nodes: nodes),
+    assigns,
+    renderer.RenderOptions(
+      encoder: fn(content) { string_builder.from_string(content) },
+      template_cache: map.from_list([
+        #(
+          "ChildTpl",
+          Template(
+            name: "ChildTpl",
+            nodes: [
+              Dynamic(If(
+                Assign("child_assign"),
+                [],
+                [Text("child_assign is false")],
+              )),
+            ],
+          ),
+        ),
+        #(
+          "points.txt.glemp",
+          Template(
+            name: "points.txt.glemp",
+            nodes: [
+              Dynamic(Output(Assign("points"))),
+              Text(" XP (level "),
+              Dynamic(Output(Assign("level"))),
+              Text(")"),
+            ],
+          ),
+        ),
+        #("some_template", Template(name: "some_template", nodes: [])),
+      ]),
+    ),
+  )
+}
+
+pub fn missing_field_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", Map(map.from_list([#("bar", String("baz"))])))
+  should.be_error(render_tpl(
+    [
+      Text("<b>"),
+      Dynamic(Output(FieldAccess(Assign("foo"), "noooooo"))),
+      Text("</b>"),
+    ],
+    assigns,
+  ))
+}
+
+pub fn out_of_bounds_test() {
+  let assigns: Assigns =
+    map.new()
+    |> map.insert("foo", List([String("bar"), String("baz")]))
+  should.be_error(render_tpl(
+    [
+      Text("<b>"),
+      Dynamic(Output(IndexAccess(Assign("foo"), 100_000))),
+      Text("</b>"),
+    ],
+    assigns,
+  ))
+}
--- a/test/text_test.gleam
+++ b/test/text_test.gleam
@ -0,0 +1,24 @@
+import gleam/map
+import gleam/string_builder
+import gleeunit/should
+import glemplate/parser
+import glemplate/text
+import glemplate/assigns
+
+pub fn encoding_test() {
+  let template = "**Welcome, <%= name %>!** <%= raw name %>"
+
+  assert Ok(tpl) = parser.parse_to_template(template, "input.txt.glemp")
+
+  let template_cache = map.new()
+  let assigns =
+    assigns.new()
+    |> assigns.add_string("name", "||<xXx_KillaBoy_69>||")
+
+  assert Ok(result) = text.render(tpl, assigns, template_cache)
+
+  should.equal(
+    string_builder.to_string(result),
+    "**Welcome, ||<xXx_KillaBoy_69>||!** ||<xXx_KillaBoy_69>||",
+  )
+}