JuliaMono - a monospaced font for scientific and technical computing

JuliaMono is a monospaced typeface designed for programming and in other text editing environments that require a wide range of specialist and technical Unicode characters. It was presented at the 2020 JuliaCon conference (which was to have been held in Lisbon, Portugal, but took place online.)

JuliaMono is:

• free

• distributed with a liberal licence ^[1]

• suitable for scientific and technical programming as well as for general purpose hacking

• full of Unicode goodness

• easy to use, simple, unquirky, friendly, and approachable

• available for MacOS, Unix, and Windows ^[2]

This site uses JuliaMono for all text; if your browser can’t^[3] (or you didn’t allow it to) download and display web fonts, you’ll only see the font in action in the images. You’ll see three large dots here when/if the font has been successfully downloaded:

To download and install JuliaMono, see the instructions here.

Screenshots

Editing code in Juno.

And in VS Code.

And in Vim:

And in Emacs:

Examples

The following examples will be rendered in JuliaMono by your browser (if it’s successfully downloaded the web font versions), so I hope what you see here is close to what I made.

The CSS markup applied to the following code also uses another weight of the typeface JuliaMono-Medium, which is a smidgeon bolder:

using Zygote: @adjoint
function ignore(f)
    try return f()
        catch e; 
        return 0;
    end
end
@adjoint function ignore(f)
    try Zygote._pullback(__context__, f)
        catch e
        0, ȳ -> nothing
    end
end

There are different weights of JuliaMono^[4], so you can control the amount of contrast you have in your highlighted code:

They all occupy the same amount of horizontal space, so they can be mixed without losing alignment.

Each of these also has a matching italic variant: so JuliaMono-Light has JuliaMono-LightItalic, and so on.

(There are also versions of two of the fonts with “Latin” in the name: these are stripped down versions supporting just the basic MacRoman/Windows1252 “Latin” character sets. You don't want to use these - they're intended for use as place-holders, of interest if you want to have more control over font loading times in web browser-based applications.)

In the hands of a virtuoso (such as Dr Zygmunt Szpak, the author of the following Julia code fragment^[5]), the range of available Unicode characters can be quite expressive:

function T(𝛉::AbstractArray,
           𝒞::Tuple{AbstractArray,
           Vararg{AbstractArray}},
           𝒟::Tuple{AbstractArray, Vararg{AbstractArray}})
    ⊗ = kron
    l = length(𝛉)
    𝐈ₗ = SMatrix{l,l}(1.0I)
    𝐈ₘ = SMatrix{1,1}(1.0I)
    𝐓 = @SMatrix zeros(l,l)
    N = length(𝒟[1])
    ℳ, ℳʹ = 𝒟
    Λ₁, Λ₂ = 𝒞
    𝚲ₙ = @MMatrix zeros(4,4)
    𝐞₁ = @SMatrix [1.0; 0.0; 0.0]
    𝐞₂ = @SMatrix [0.0; 1.0; 0.0]
    for n = 1:N
        index = SVector(1,2)
        𝚲ₙ[1:2,1:2] .=  Λ₁[n][index,index]
        𝚲ₙ[3:4,3:4] .=  Λ₂[n][index,index]
        𝐦    = hom(ℳ[n])
        𝐦ʹ   = hom(ℳʹ[n])
        𝐔ₙ   = (𝐦 ⊗ 𝐦ʹ)
        ∂ₓ𝐮ₙ = [(𝐞₁ ⊗ 𝐦ʹ) (𝐞₂ ⊗ 𝐦ʹ) (𝐦 ⊗ 𝐞₁) (𝐦 ⊗ 𝐞₂)]
        𝐁ₙ   = ∂ₓ𝐮ₙ * 𝚲ₙ * ∂ₓ𝐮ₙ'
        𝚺ₙ   = 𝛉' * 𝐁ₙ * 𝛉
        𝚺ₙ⁻¹ = inv(𝚺ₙ)
        𝐓₁   = @SMatrix zeros(Float64,l,l)
        for k = 1:l
            𝐞ₖ = 𝐈ₗ[:,k]
            ∂𝐞ₖ𝚺ₙ = (𝐈ₘ ⊗ 𝐞ₖ') * 𝐁ₙ * (𝐈ₘ ⊗ 𝛉) + (𝐈ₘ ⊗ 𝛉') * 𝐁ₙ * (𝐈ₘ ⊗ 𝐞ₖ)
            # Accumulating the result in 𝐓₁ allocates memory,
            # even though the two terms in the
            # summation are both SArrays.
            𝐓₁ = 𝐓₁ + 𝐔ₙ * 𝚺ₙ⁻¹ * (∂𝐞ₖ𝚺ₙ) * 𝚺ₙ⁻¹ * 𝐔ₙ' * 𝛉 * 𝐞ₖ'
        end
        𝐓 = 𝐓 + 𝐓₁
    end
    𝐓
end

Languages

Here are some samples of various languages^[6] :

Unicode coverage

Here's a sample of some of the Unicode glyphs provided:

One of the goals of JuliaMono is to include most of the characters that a typical programmer or monospaced-font user would reasonably expect to find. (Except for all those emojis - they are best handled by the operating system.) Here's a few less common ones:

You can see a complete list of glyphs on the Glyphs page (caution: it's quite a large page). If you want a more flexible way of finding out about JuliaMono's Unicode support, you can visit glyphy.info and type a name (eg interrobang) or a hexadecimal number (eg 0x203d) to see matching characters. If the glyph is present in JuliaMono, you'll see a checkmark ✓:

If you're using the Julia language, you can also do this in the Julia REPL. Install the registered Glyphy.jl package in the usual way, and then run it like this:

julia> using Glyphy

julia> glyphy("interrobang")

0203d   ‽   ✓    interrobang
02e18   ⸘   ✓    inverted interrobang
1f679   🙹   ✓    heavy interrobang ornament
1f67a   🙺   ✓    sans-serif interrobang ornament
1f67b   🙻   ✓    heavy sans-serif interrobang ornament
 found 5 glyphs matching "interrobang"

julia> glyphy(0x203d)

0203d   ‽   ✓    interrobang

Mono space

In JuliaMono, every character is the same width, because this is a monospaced typeface. Usually, typefaces with a lot of Unicode mathematical symbols are not monospaced, because they’re intended for use in prose and \( \LaTeX \) applications, rather than in programming code. You probably want ∑s in your code rather than \( \sum \)s, because the big ones will upset your formatting.

From a design perspective, forcing every character into the same size box is a problem. It’s like fitting every human being of whatever shape or size into identical airplane seats - some characters are bound to look uncomfortable. There’s never quite enough room for a nice-looking “m” or “w”.

The Julia package UnicodePlots.jl uses various Unicode characters to plot figures directly in a terminal window. ^[7]

It’s also a good idea to support box-drawing characters, such as the ones used for displaying DataFrames.jl output (terminal permitting):

julia> df = DataFrame(A=samples, B=glyphs)
df = 10×2 DataFrame
│ Row │ A              │ B                   │
│     │ String         │ String              │
├─────┼────────────────┼─────────────────────┤
│ 1   │ sample 1       │ ▁▂▁▁▂▄▅▁▄▁▁▅▆▂▇▅▂▇  │
│ 2   │ sample 2       │ ▁▂▄▁▁▃▁▆▂▆▃▁▂▃▂▇▄   │
│ 3   │ sample 3       │ ▁▆▇▁▃▇▇▆▅▅▄▇▇▅▅▇▄▂  │
│ 4   │ sample 4       │ ▅▁▄▁▆▃▁▃▇▂▂▇▅▇▃▆▃▁  │
│ 5   │ sample 5       │ ▆▂▁▂▇▆▃▅▅▄▆▇▄▇▆▁▇   │
│ 6   │ sample 6       │ ▁▁▇▂▂▇▃▅▂▂▆▂▄▄▁▄▂▇▆ │
│ 7   │ sample 7       │ ▂▃▂▁▁▇▁▂▆▂▁▇▁▄▃▂▁▄  │
│ 8   │ sample 8       │ ▄▄▁▂▄▁▅▁▅▁▂▂▇▂▁▃▄▄  │
│ 9   │ sample 9       │ ▁▁▁▂▁▆▃▄▄▁▂▂▃▂▁▅▁▆▃ │
│ 10  │ sample 10      │ ▁▇▄▂▅▃▇▁▇▇▆▄▇▅▄▂▄▅▄ │

(Can you spot the little used and sadly mathematically-unsupported “times” (×) character?)

For a comparison of JuliaMono with other math-capable monospaced fonts, visit mono-math.netlify.app, which shows how Unicode math symbols look.

JuliaMono is quite greedy^[8], and contains quite a few Unicode glyphs.

(Of course, size isn’t everything - quality can beat quantity, and other fonts will offer different experiences^[9]).

For Julia users, if you want to know whether you can use a Unicode character as an identifier in your Julia code, use the undocumented function Base.isidentifier(). So, for example, if you have the urge to use a dingbat (one of the classic Herman Zapf dingbat designs) as a variable name, you could look for something suitable in the output of this:

julia>  for n in 0x2700:0x27bf
			Base.isidentifier(string(Char(n))) && print(Char(n))
	    end
✀✁✂✃✄✅✆✇✈✉✊✋✌✍✎✏✐✑✒✓✔✕✖✗✘✙✚✛✜✝✞✟✠✡✢✣✤✥✦✧✨✩✪✫✬✭✮✯✰✱✲✳✴✵✶✷✸✹✺
✻✼✽✾✿❀❁❂❃❄❅❆❇❈❉❊❋❌❍❎❏❐❑❒❓❔❕❖❗❘❙❚❛❜❝❞❟❠❡❢❣❤❥❦❧➔➕➖➗➘➙➚➛➜➝➞➟➠➡
➢➣➤➥➦➧➨➩➪➫➬➭➮➯➰➱➲➳➴➵➶➷➸➹➺➻➼➽➾➿

julia> ❤(s) = println("I ❤ $(s)")
❤ (generic function with 1 method)

julia> ❤("Julia")
I ❤ Julia

Contextual and stylistic alternates (“ligatures”)

JuliaMono is an OpenType typeface. OpenType technology provides powerful text positioning, pattern matching, and glyph substitution features, which are essential for languages such as Arabic and Urdu. In English, OpenType features are often seen when letter pairs such as fi in certain fonts are replaced by a single glyph such as fi. These alternatives, often referred to generally as ‘ligatures’ have been used ever since printing with moveable type was invented, replacing the occasional awkward character combination with a better-looking alternative.

If you love lots of programming-oriented ligatures, you should probably use Fira Code, a version of Mozilla’s Fira Mono font with literally hundreds of extra ligatures. I’m not a big fan of their use in coding fonts (and I’m not the only one^[10]). I like to see exactly what I’ve typed, rather than what the font has decided to replace it with.

Some languages, such as Julia, are designed to use Unicode characters, and so many ligatures aren't usually needed, but there are a few places where the obvious Unicode glyphs are not accepted by the language, where the ASCII-art substitutes can be improved by the judicious use of alternate glyphs. There are also a few places where some subtle tweaks can enhance readability without introducing ambiguity.

Contextual alternates

In JuliaMono, the following substitutions (‘ligatures’) are applied when the contextual alternates feature (calt) is active:

You can see some of these in action in the following code fragment:^[11]

julialang = true # (!= 0)
(x, y) -> (x + y)
f(p::Int) = p * p
@inbounds if f in (Base.:+, Base.:-)
    if any(x -> x <: AbstractArray{<:Number})
        nouns = Dict(
            Base.:+ => "addition",
            Base.:- => "subtraction",
        )
    end
end
df2 = df |>
    @groupby(_.a) |>
    @map({a = key(_), b = mean(_.b)}) |>
    DataFrame # <|

Stylistic sets

OpenType fonts also offer you the ability to choose different designs for certain characters. These are stored as ‘stylistic sets’.

All these options are stored in the font, and are often referred to by their internal four letter code (not the best user-oriented design, really). For example, the contextual alternates listed above are collectively stored in the calt feature.

Sometimes, an application will show the options more visually in a Typography panel^[12], usually tucked away somewhere on a Font chooser dialog.

Here’s a list of the stylistic sets currently available in JuliaMono.

Some character variations are provided in cv.. features.

All this fancy technology is under the control of the application and the operating system you’re using. Ideally, they will provide an easy way for you to switch the various OpenType features on and off.

Browser-based editors such as VS Code support many OpenType features in their editor windows, but not so much in the terminal emulator/console windows. They provide a settings area where you can type CSS or JSON selectors to control the appearance of features, and you’ll have to know the feature codes. (See this section.) Some features are opt in, others are opt out; this too can vary from application to application.

Terminal/console applications also vary a lot. wezterm is cross-platform and provides excellent font support. On MacOS the Terminal and iTerm applications try to offer controls for OpenType features, with varying degrees of success. On Linux, some terminal applications such as Konsole and Kitty offer quite good OpenType support, but others such as Alacritty offer little or none, as yet. ^[13]

If the application allows, you should be able to switch the calt contextual ligatures off, particularly since a few people won’t like any of them in their code.

You can swtich the calt set off using CSS (see here). You can enable one or more of the alternative stylistic sets.

Off (calt off, no stylistic sets):

julialang = true # (!= 0) -->
(x, y) -> (x + y)
f(p::Int) = p .* p[[1, 2, 3], [4, 5, 6]]
@inbounds if f in (Base.:+, Base.:-)
    if any(x -> x <: AbstractArray{<:Number})
        nouns = Dict(
            Base.:+ => "addition",
            Base.:- => "subtraction",
        )
    end
end
df2 = df |>
    @groupby(_.a) |>
    @map({a = key(_), b = mean(_.b)}) |>
    DataFrame # <|

On (calt on, most stylistic sets on):

julialang = true # (!= 0) -->
(x, y) -> (x + y)
f(p::Int) = p .* p[[1, 2, 3], [4, 5, 6]]
@inbounds if f in (Base.:+, Base.:-)
    if any(x -> x <: AbstractArray{<:Number})
         nouns = Dict(
            Base.:+ => "addition",
            Base.:- => "subtraction",
        )
    end
end
df2 = df |>
    @groupby(_.a) |>
    @map({a = key(_), b = mean(_.b)}) |>
    DataFrame # <|

Mathematical script styles: Calligraphers vs Roundhanders

By default, mathematical script characters (starting at Unicode U+1d49C) are drawn in Cursive, a basic calligraphy style.

By switching to the stylistic set ss15, these characters change from Cursive:

to use an old English script style known as “roundhand”:

Here’s a comparison of the two script styles in context - the default Cursive on top, ss15’s Roundhand below - as rendered in a \( \LaTeX \) document.

(This code snippet is from the Algorithms Handbook, by Mykel J. Kochenderfer, Tim A. Wheeler, and Kyle Wray, which uses JuliaMono for the code samples.)

As with all things typographical, the ease with which you recognize characters depends to some extent on your personal experiences and education; I suspect that few people today learn or practice the roundhand style, and some of the shapes will be unfamiliar. You may also find the more detailed forms more difficult to read on lower-resolution displays.

Variation selectors

The Unicode system provides a mechanism whereby characters can be followed by other modifier characters that change the appearance of the preceding one. Some of these variation selectors, known as VS1, VS2, have code points starting at U+FE00. The Unicode Consortium has defined variation selectors that change the style of capital mathematical script letters from Cursive to Roundhand.

(See the Unicode Consortium PDF L2/20-275R.)

So if you type a capital letter A to Z in the range U+1D49C .. U+1D4B5 (with - this being Unicode - some deviations into U+210B .. 2133 for H, I, L, R, B, E, F, M) - and then follow it with VS2 (U+FE01), the character is supposed to be rendered in Roundhand, not Cursive:

1D49C         -> 𝓐
1D49C FE01    -> 𝓐︁

Customizing the font

It’s possible that you don’t like the ligatures and contextual alternate characters provided in JuliaMono. Or perhaps the application you want to use won't let you access some of the features that you'd like to see.

There are various ways you can customize the TTF font files so that they have the features you require.

Using FontFreeze

The FontFreeze online web application allows you to create and download a customized instance of a font that has various OpenType features permanently switched on or off, so that you can use the font's features in those inadequate applications.

Visit https://mutsuntsai.github.io/fontfreeze/ for details.

Using pyftsubset

You can do a similar job on your computer by following these instructions for using pyftsubset, which lets you strip features out of the font (courtesy of @fredrikekre):

$ cat Dockerfile
FROM python
RUN pip install fonttools
COPY run.sh /scripts/
ENTRYPOINT ["/scripts/run.sh"]

$ cat run.sh
#!/bin/bash
set -euo pipefail

VERSION="${1-}"

mkdir -p /juliamono-source
mkdir -p /juliamono-output
mkdir -p /juliamono

# Download release version
curl -L "https://github.com/cormullion/juliamono/releases/download/v${VERSION}/JuliaMono.tar.gz" | tar -xzvC /juliamono-source

# Strip glyphs
for f in /juliamono-source/*.ttf
do
    pyftsubset "$f" '*' --output-file=/juliamono-output/$(basename "$f")  --layout-features-=calt,liga
done

# Pack it up
tar -C /juliamono-output -czvf /juliamono/JuliaMono-${VERSION}.tar.gz $(ls /juliamono-output)

$ cat Makefile
.PHONY: image strip
VERSION := 0.021
image:
        docker build -t juliamono-strip:latest .

strip:
        docker run --rm -v ${PWD}:/juliamono juliamono-strip:latest "${VERSION}"

There are a few areas of the Unicode system that have been officially kept empty and are thus available to store characters that are not part of the official standard. These are called the Private Use Areas, and there are three: \ue000 to \uf8ff, \UF0000 to \UFFFFD, and U100000 to U+10FFFD.

Each typeface can do its own thing in these areas. In JuliaMono you’ll find these, among others, and if you ask nicely I might add some more:

The obvious drawback to using characters in a Private Use Area is that you have to have installed the font wherever you want to see them rendered correctly, unless they’ve been converted to outlines or bitmaps. If the font isn’t installed (eg on github), you have no idea what glyph - if any - will be displayed.

Julia users: you can define these to be available at the REPL. For example, say you want the Julia dots to be available in the terminal when you type \julialogo in a Julia session with the JuliaMono font active. Run this:

using REPL
REPL.REPLCompletions.latex_symbols["\\julialogo"] = "\ue800"

Now you can insert the logo in strings by typing \julialogo :

julia> println("Welcome to ")
Welcome to 

It’s usually possible to type Unicode values directly into text. This is a useful skill to have when you’re not using a capable REPL. On MacOS you hold the Option (⌥) key down while typing the four hex digits (make sure you’re using the Unicode Hex Input keyboard). On Windows I think you type the four hex digits followed by ALT then X. On Linux it might be ctrl-shift-u followed by the hex digits.

Thanks!

Thanks to: Thibaut Lienart for his Franklin.jl web site builder; to Jérémie Knüsel who provided invaluable suggestions and advice; to Dr Zygmunt Szpak for his cool maths code; to Simeon Schaub for the issues and PRs, and to others in the Julia community for help and suggestions. Type sample from underscoretype.

Footnotes