ANSI themes

Smalto renders syntax-highlighted text with ANSI terminal color codes. The AnsiTheme type lets you control which colors are applied to each token type.

Default theme

The default theme applies these colors:

Token	Style
Keyword	Yellow
String	Green
Number	Green
Function	Blue
Comment	Gray italic
Module	Cyan
Type	Cyan
Operator	Magenta
Punctuation	Gray
Tag	Red
Builtin	Bright blue
Attribute	Yellow
Property	Yellow
Selector	Cyan
Regex	Green
Constant	Bright magenta
Variable	Bright yellow
Whitespace	No styling
Other	No styling
Custom	No styling (see below)

The default theme also includes styles for markup tokens commonly produced by the Markdown grammar:

Custom token	Style
`important`	Bold bright yellow
`bold`	Bold
`italic`	Italic
`strike`	Strikethrough
`code`	Green
`url`	Underline cyan

Use smalto.to_ansi() to render with the default theme:

import smalto
import smalto/languages/python

let colored = smalto.to_ansi("print('hello')", python.grammar())

Custom themes

Build a custom theme with ansi_theme.new() and per-token setter functions:

import gleam_community/ansi
import smalto
import smalto/ansi_theme
import smalto/languages/python

let theme =
  ansi_theme.new()
  |> ansi_theme.keyword(ansi.bright_magenta)
  |> ansi_theme.string(ansi.bright_green)
  |> ansi_theme.number(ansi.bright_yellow)
  |> ansi_theme.function(ansi.bright_cyan)
  |> ansi_theme.comment(fn(v) { ansi.italic(ansi.bright_black(v)) })
  |> ansi_theme.operator(ansi.red)

let colored = smalto.to_ansi_with("print('hello')", python.grammar(), theme)

Tokens without a setter in the theme are rendered as plain text.

Setter functions

Each setter takes the theme and a styling function fn(String) -> String:

Setter	Token type
`ansi_theme.keyword(theme, style)`	Keywords
`ansi_theme.string(theme, style)`	String literals
`ansi_theme.number(theme, style)`	Numbers
`ansi_theme.comment(theme, style)`	Comments
`ansi_theme.function(theme, style)`	Function names
`ansi_theme.operator(theme, style)`	Operators
`ansi_theme.punctuation(theme, style)`	Punctuation
`ansi_theme.type_(theme, style)`	Type names
`ansi_theme.module(theme, style)`	Module names
`ansi_theme.variable(theme, style)`	Variables
`ansi_theme.constant(theme, style)`	Constants
`ansi_theme.builtin(theme, style)`	Built-in functions
`ansi_theme.tag(theme, style)`	HTML/XML tags
`ansi_theme.attribute(theme, style)`	Attributes
`ansi_theme.selector(theme, style)`	CSS selectors
`ansi_theme.property(theme, style)`	Properties
`ansi_theme.regex(theme, style)`	Regular expressions
`ansi_theme.whitespace(theme, style)`	Whitespace
`ansi_theme.other(theme, style)`	Unmatched text
`ansi_theme.custom(theme, name, style)`	Custom token by name

Composing styles

The styling function is fn(String) -> String, so you can compose multiple ANSI effects:

import gleam_community/ansi

// Bold cyan
ansi_theme.keyword(theme, fn(v) { ansi.bold(ansi.cyan(v)) })

// Italic gray (like the default comment style)
ansi_theme.comment(theme, fn(v) { ansi.italic(ansi.gray(v)) })

// Underlined bright red
ansi_theme.tag(theme, fn(v) { ansi.underline(ansi.bright_red(v)) })

Extending the default theme

Start from the default and override specific tokens:

import gleam_community/ansi
import smalto/ansi_theme

let theme =
  ansi_theme.default()
  |> ansi_theme.keyword(ansi.bright_magenta)
  |> ansi_theme.comment(fn(v) { ansi.italic(ansi.bright_black(v)) })

Custom token styles

Grammars may produce Custom tokens for language-specific categories. Style them with ansi_theme.custom():

import gleam_community/ansi
import smalto/ansi_theme

let theme =
  ansi_theme.default()
  |> ansi_theme.custom("decorator", ansi.bright_yellow)
  |> ansi_theme.custom("annotation", ansi.bright_cyan)