Error handling

All Blogatto build functions return Result(Nil, BlogattoError). The library never panics — every failure is surfaced as a Result.

BlogattoError variants

Variant	Payload	Description
`DevServer(String)`	Error message	An error occurred in the development server (e.g. file watching, live reload)
`File(FileError)`	`simplifile.FileError`	File system error (reading, writing, deleting files or directories)
`FrontmatterMissing`	—	A markdown file has no frontmatter block
`FrontmatterMissingField(String)`	Field name	A required frontmatter field (`title`, `date`, or `description`) is missing
`FrontmatterInvalidDate(String)`	The date string	The `date` field could not be parsed as `YYYY-MM-DD HH:MM:SS`
`FrontmatterInvalidLine(String)`	The line content	A frontmatter line could not be parsed as a `key: value` pair
`InvalidUri(String)`	The invalid URI string	A URI could not be parsed during URL resolution

Handling errors

Basic pattern

import blogatto
import blogatto/error
import gleam/io

case blogatto.build(cfg) {
  Ok(Nil) -> io.println("Site built successfully!")
  Error(err) -> {
    io.println("Build failed: " <> error.describe_error(err))
    // Exit with error code, log to monitoring, etc.
  }
}

Matching specific errors

import blogatto
import blogatto/error
import gleam/io

case blogatto.build(cfg) {
  Ok(Nil) -> io.println("Done!")
  Error(error.FrontmatterMissingField(field)) ->
    io.println("A post is missing the '" <> field <> "' field in its frontmatter")
  Error(error.FrontmatterInvalidDate(date)) ->
    io.println("Invalid date format: '" <> date <> "'. Use YYYY-MM-DD HH:MM:SS")
  Error(error.FrontmatterMissing) ->
    io.println("A markdown file is missing its frontmatter block")
  Error(err) ->
    io.println("Build failed: " <> error.describe_error(err))
}

describe_error

The error.describe_error(error) function converts any BlogattoError into a human-readable string:

import blogatto/error

error.describe_error(error.FrontmatterMissingField("title"))
// -> "Frontmatter missing required field: title"

error.describe_error(error.FrontmatterInvalidDate("not-a-date"))
// -> "Frontmatter has invalid date format: not-a-date"

error.describe_error(error.InvalidUri(":::bad"))
// -> "Invalid URI: :::bad"

Common issues

Missing frontmatter

Every markdown file must start with a --- delimited frontmatter block. Files without frontmatter produce FrontmatterMissing.

Fix: Add frontmatter to the top of the file:

---
title: My Post
date: 2025-01-15 00:00:00
description: A short description
---

Invalid date format

The date field must follow YYYY-MM-DD HH:MM:SS format exactly.

Valid: 2025-01-15 00:00:00

Invalid: 2025-01-15, Jan 15, 2025, 2025/01/15 00:00:00

File permission errors

File(Eacces) indicates a permissions issue reading source files or writing to the output directory.

Fix: Ensure the output directory’s parent is writable and source files are readable.

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