Making DSLs in F#

The article presents a simple F# DSL for software estimation and project planning. It uses English-like statements to define a project, add resources, group tasks, assign durations, and then generate a Microsoft Project plan.

Reading notes

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• The article defines a DSL as a way to express domain-specific logic in English instead of a programming language.
• The example domain is software estimation, with a real-world version already used at the author’s company.
• The attached code is a single .fs file and requires Project 2007 to run.
• The problem described is estimating software work from an RFP by breaking a project into tasks, durations, resources, and milestones.
• The DSL is meant to save time compared with drawing and rearranging a Gantt chart in Microsoft Project.
• It also lets business logic and validation rules be embedded in the planning procedure.
• The target users are project managers who may not know programming but can work with a DSL.
• The article presents F# as a good choice because it is a first-class .NET language and can be used to build the needed infrastructure.
• The first statement shown defines a project name and start date, and it maps to a Project type with mutable fields.
• The DSL keeps one project in a global variable called my_project.
• A project function initializes the project name, empty resource and group lists, and parses the start date.
• Resources are modeled with a Resource type containing name, position, and rate.
• A resource statement creates a resource and prepends it to the project’s resource list.
• The article notes that list items end up in reverse order and are later reversed when needed.
• A group statement links a task group to a named resource using string lookup over the project’s resource list.
• Tasks are modeled with a Task type containing name and duration.
• Time units are represented by constants such as hours, days, weeks, and months so that task ... takes ... reads fluently.
• The task function formats duration values for Project and adds each task to the current group.
• The current task is found as the head of the list because new tasks are prepended.
• The prepare function creates a Project application, adds the project, copies resources, creates group tasks, and links task predecessors.
• The article ends with a complete sample script that defines resources, groups, tasks, and finishes with prepare my_project.