syntax: add Gleam language support by HiwarkhedePrasad · Pull Request #4045 · micro-editor/micro

HiwarkhedePrasad · 2026-03-15T18:20:59Z

Adds syntax highlighting for the Gleam programming language.

Supports:

Keywords (fn, let, case, if, else, import, pub, type, opaque, const, use)
Built-in types (Int, Float, String, Bool, List, Option, Result, Nil)
Constants (True, False, Nil)
Single line comments (//)
Strings
Numbers

Andriamanitra

Good start but needs some work. I would consider adding highlighting for attributes (@external/@deprecated).

Andriamanitra · 2026-03-16T01:12:08Z

runtime/syntax/gleam.yaml

+      start: "\""
+      end: "\""
+      skip: "\\\\."
+  - special: "\\b[0-9]+\\.?[0-9]*\\b"


Numbers should be constant.number. Gleam also supports a pretty wide range of number literals ¹ that this regex doesn't cover. The formats seem to be similar to eg. Python so we can probably just copy them from the Python syntax:

micro/runtime/syntax/python3.yaml

Lines 28 to 32 in 42d0ddf

# numbers

- constant.number: "\\b[0-9](_?[0-9])*(\\.([0-9](_?[0-9])*)?)?(e[0-9](_?[0-9])*)?\\b" # decimal

- constant.number: "\\b0b(_?[01])+\\b" # bin

- constant.number: "\\b0o(_?[0-7])+\\b" # oct

- constant.number: "\\b0x(_?[0-9a-fA-F])+\\b" # hex

Footnotes

https://tour.gleam.run/everything/#basics-number-formats ↩

Andriamanitra · 2026-03-16T01:16:14Z

runtime/syntax/gleam.yaml

+      end: "\""
+      skip: "\\\\."
+  - special: "\\b[0-9]+\\.?[0-9]*\\b"
+  - type: "\\b[A-Z][a-zA-Z0-9_]*\\b"


This overlaps with the definitions for identifier and constant above so those will get colored as type. To fix it you can put this rule before them (later rules are applied on top of earlier ones). It would also make sense to me to change this rule to be identifier, and use type for the built-in types (Int, Float, etc.) that are currently identifier.

Andriamanitra · 2026-03-16T01:16:58Z

runtime/syntax/gleam.yaml

+
+rules:
+  - statement: "\\b(fn|let|case|if|use|import|pub|type|opaque|const|as|assert|panic|todo|echo)\\b"
+  - identifier: "\\b(Int|Float|String|Bool|List|Option|Result|Nil|BitArray)\\b"


I would remove Nil from here since it's also in constant.

Andriamanitra · 2026-03-16T01:32:07Z

runtime/syntax/gleam.yaml

+  - statement: "\\b(fn|let|case|if|use|import|pub|type|opaque|const|as|assert|panic|todo|echo)\\b"
+  - identifier: "\\b(Int|Float|String|Bool|List|Option|Result|Nil|BitArray)\\b"
+  - constant: "\\b(True|False|Nil)\\b"
+  - operator: "(\\|>|->|<>|==|!=|<=|>=|&&|\\|\\|)"


Most syntaxes choose to use statement for operators (to color them red in the default colorscheme). Most built-in colorschemes color operator with the default (white) color. The list is missing assignment and arithmetic operators.

Hi @Andriamanitra , thanks for the great feedback! I've pushed a new commit that addresses all your points:

Rule Overlap: Moved the base identifier rule to the top, so the specific type and constant rules below it can correctly overwrite it.

Built-in Types: Removed Nil from the built-in types list (kept it under constants).

Operators: Moved operators to statement so they highlight correctly, and added the missing arithmetic, assignment, and Gleam-specific float operators.

Numbers: Implemented the robust number regexes from the Python syntax file to handle binary, octal, hex, and scientific notation floats.

Attributes: Added a preproc rule (@[a-zA-Z0-9_]+) to highlight attributes like @external and @deprecated.

…tributes

Andriamanitra

It's working pretty good now but I noticed a couple more issues while testing the syntax with the Gleam code from https://learnxinyminutes.com/gleam

Number literals with underscores
Float comparisons (<., <=., etc.)
Escapes in strings (eg. "\"")
Tuples (eg. #(1, 2))

I don't think commenting the file is necessary, the comments are mostly redundant or irrelevant.

Andriamanitra · 2026-03-16T12:29:24Z

runtime/syntax/gleam.yaml

+  - statement: "\\b(fn|let|case|if|use|import|pub|type|opaque|const|as|assert|panic|todo|echo)\\b"
+
+  # 5. Attributes / Decorators (Added for @external, @deprecated, etc.)
+  - preproc: "@[a-zA-Z0-9_]+"


I think this is too permissive. I'm not sure if Gleam even has anything besides @external and @deprecated right now but if we follow vim's example we should only allow lowercase here: ¹

Suggested change

- preproc: "@[a-zA-Z0-9_]+"

- preproc: "@[a-z][a-z_]*"

Footnotes

https://github.com/vim/vim/blob/e21c4a649a830716599eadebad04ddf2393230bc/runtime/syntax/gleam.vim#L65 ↩

Andriamanitra · 2026-03-16T12:33:08Z

runtime/syntax/gleam.yaml

+  # 7. Numbers (Copied directly from Python's robust micro syntax as the maintainer requested)
+  - constant.number: "\\b0b[01]+\\b"
+  - constant.number: "\\b0o[0-7]+\\b"
+  - constant.number: "\\b0x[0-9a-fA-F]+\\b"
+  - constant.number: "\\b[0-9]+\\.[0-9]*([eE][+-]?[0-9]+)?\\b"
+  - constant.number: "\\b[0-9]+\\b"


Contrary to what the comment claims these are not copied from Python, they're missing support for underscores.

Andriamanitra · 2026-03-16T12:44:23Z

runtime/syntax/gleam.yaml

+      skip: "\\\\."
+


Suggested change

skip: "\\\\."

skip: "\\\\."

rules:

- constant.specialChar: "\\\\."

Hi @Andriamanitra, thanks again for the detailed feedback! I've made all the suggested changes:

Numbers now support underscores (e.g., 1_000_000)

Added float comparison operators (<., >., <=., >=.)

String escapes are now highlighted as special characters

Added tuple syntax #(...) highlighting

Attributes are now restricted to lowercase only

Andriamanitra

The last commit broke the whole thing by removing the required filetype:.

HiwarkhedePrasad · 2026-03-16T16:55:52Z

Sorry about that, fixed in the latest commit — restored the filetype: gleam field and also cleaned up the inline comments while I was at it.

Andriamanitra

Everything seems to work fine now. The tuple highlighting looks a bit weird because the opening paren is colored but the closing one is not but I guess it's fine.

JoeKar · 2026-03-18T20:10:57Z

Everything seems to work fine now. The tuple highlighting looks a bit weird because the opening paren is colored but the closing one is not but I guess it's fine.

Maybe we could try it with a region (like in the html.yaml):

    - default:
        start: "#\\("
        end: "\\)"
        limit-group: special
        rules:
            - constant.number: "\\b0b[01](_?[01])*\\b"
            - constant.number: "\\b0o[0-7](_?[0-7])*\\b"
            - constant.number: "\\b0x[0-9a-fA-F](_?[0-9a-fA-F])*\\b"
            - constant.number: "\\b[0-9](_?[0-9])*(\\.[0-9](_?[0-9])*)?([eE][+-]?[0-9](_?[0-9])*)?\\b"
            - constant.string:
                start: '"'
                end: '"'
                skip: "\\\\."
                rules:
                    - constant.specialChar: "\\\\."

Yes, it duplicates rules, but we can't include the same type, because this would lead to recursion.

BTW:
Looks like we've inconsistent (2-space and 4-space) indentation.

HiwarkhedePrasad added 2 commits March 15, 2026 23:44

syntax: add Gleam language support

e19c021

syntax: improve Gleam syntax highlighting

992f30c

Andriamanitra suggested changes Mar 16, 2026

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Andriamanitra reviewed Mar 16, 2026

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Refactor Gleam syntax: fix overlaps, expand numbers/operators, add at…

aa2c965

…tributes

Andriamanitra reviewed Mar 16, 2026

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syntax: refine Gleam syntax with review fixes

b6657ad

Andriamanitra suggested changes Mar 16, 2026

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syntax: restore missing filetype field and remove comments

5f594d1

Andriamanitra approved these changes Mar 17, 2026

View reviewed changes

	# numbers
	- constant.number: "\\b[0-9](_?[0-9])(\\.([0-9](_?[0-9]))?)?(e[0-9](_?[0-9])*)?\\b" # decimal
	- constant.number: "\\b0b(_?[01])+\\b" # bin
	- constant.number: "\\b0o(_?[0-7])+\\b" # oct
	- constant.number: "\\b0x(_?[0-9a-fA-F])+\\b" # hex

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HiwarkhedePrasad commented Mar 15, 2026

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HiwarkhedePrasad Mar 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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HiwarkhedePrasad commented Mar 16, 2026

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JoeKar commented Mar 18, 2026

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HiwarkhedePrasad Mar 16, 2026 •

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