write-nanoflows

Find it fast

sed -n '<from>,<to>p' SKILL.md one section rather than reading the file; ./mxcli syntax <topic> answers how do I write this for a fraction of either.

lines	section
35-44	When to Use This Skill
45-78	Changing an Existing Nanoflow
79-97	When to Use a Nanoflow vs a Microflow
98-112	Key Differences from Microflows
113-136	Nanoflow Structure
137-145	Naming Convention
146-214	Supported Activities
215-481	Real-World Patterns
482-552	NanoflowCommons JavaScript Actions Reference
553-591	Disallowed Activities
592-595	Return Type Restrictions
596-640	Error Handling in Nanoflows
641-648	Security (GRANT/REVOKE)
649-661	Management Commands
662-672	Common Mistakes
673-687	Validation Checklist

Mendix Nanoflow Skill

This skill provides guidance for writing Mendix nanoflows in MDL syntax. Nanoflows share syntax with microflows but execute client-side with restricted capabilities.

When to Use This Skill

Use this skill when:

• Writing CREATE NANOFLOW statements
• Debugging nanoflow validation errors
• Understanding nanoflow restrictions vs microflows
• Building mobile or offline-capable features

If you're not sure whether the logic belongs in a nanoflow or a microflow, read the next section first. The mirror lives in write-microflows — keep both copies in sync.

Changing an Existing Nanoflow

Choose the mode by who owns the nanoflow (choose-edit-mode):

• Created by your MDL scripts, and not edited in Studio Pro since: edit the script (or fresh describe output) and re-run create or modify.
• Authored in Studio Pro: prefer alter nanoflow X { insert/replace/drop … } (targets by output variable, caption or statement pattern). create or modify of describe output also works as a patch: an unchanged definition writes nothing, and an inserted, replaced or dropped statement (at the top level or in an if branch) is spliced in, leaving every other node, merge and curve as stored — a guard clause (if … then return; end if;) too, its return a new end event, and so is the return ending a new activity's error handler; a changed return value or if condition is set on the stored end event or decision, and a body without a trailing return means the stored end. The header (documentation, return type, parameters added, retyped or — when unused — removed) is set on the stored document, and a stated @position or @start moves the stored node, keeping its flows. A change it cannot patch — anything inside a loop body or error handler, a redrawn @anchor/@curve, any other return added or taken away — rebuilds the whole nanoflow under mdl 0 (warning MDL-V1-REBUILD: element IDs renumbered, merges removed, curves reset) and is refused under mdl 1;.
• Rebuilding deliberately: drop nanoflow X; and create nanoflow X … in ONE script. The drop's module-role grants (and the unit's ID and folder) carry only to a create later in the same script or REPL session; a drop in one run and a create in the next loses every grant execute. drop prints the roles it removed and the grant to restore them.
• Changing something inside a loop body (either owner) : an activity replaced by one of the same kind (new values, same statements in the same order) is spliced in place by both create or modify and alter. Anything else — a statement added, removed, reordered or moved — neither can make: replace the whole loop, addressed by its handle, with the body as it should be (replace loop $Item in $Items with begin loop $Item in $Items begin … end loop; end;). Everything outside the loop keeps its $IDs, positions and curves; the loop and its body are rebuilt. For a nested loop, replace the outer one.