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Interview Presentation

Unified Guided Expressions

Drew Polstra
Candidate for Staff Full-Stack Software Engineer, Atlas Applications
Boston Dynamics · April 7, 2026

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Prologue

The Skunkworks

I'm asked to build a secret prototype of an unrelated project.

Shown to the head of engineering. He loves it. "Who made this?"

He steals me and redirects me to a new, critical project — Unified Guided Expressions.

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Guided Expressions

Interactive concept demo — build an expression, then click a test record to evaluate it

Expression

Test Records

click a row to evaluate

First Name	Last Name	Employer	Fav. Color	Salary	Result

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Prior Attempts

Two teams were intended as users of the Guided Expression Editor, but they had different ideas of how it should work.

BRE Team

Business Rules Environment

XML Weakly Typed

"Fill anywhere." Flexible, tolerant of ambiguity. Users jump around, leave things incomplete. Built-in test data evaluation.

vs.

MDH Team

Metadata Hub

JSON Strongly Typed

"Guided, left-to-right." Strict contracts, every field validated before moving on. No tolerance for error states. No test data feature.

Attempt 1 — Shared Widget. Teams shared only the lowest-level UI component — a basic boolean-logic tree that defines groups and clauses, but not storage, interaction patterns, or anything else. Massive differences layered on top.

Attempt 2 — JSON in XML. Dropped MDH's JSON directly into BRE's XML tree. Broke BRE's assumptions, especially test data plumbing.

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Dark Night of the Soul

I investigate.

I consult with experts across both teams. They all tell me it can't be done.

My manager bucks me up — we have to do this, so find a way.

I arrive at an insight: "We'll definitely need a transpiler. Let's start there."

Start with the easy case — down-transpile from MDH to BRE format. Strong typing to weak.

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The Big Meeting

Night before: I slap a demo frontend on the prototype transpiler.

Big personalities in the room. Lots of opinions. Bickering.

I show the demo.

The room coalesces in real time. The transpiler shows a clear path forward.

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Making It Real

Up-transpile, inference, and philosophical tension playing out in the edge cases.

BRE Philosophy

"Fill anywhere." High tolerance for partial and error states. Users can jump around freely.

vs.

MDH Philosophy

"Guided, left-to-right." Every field validated before moving on. No tolerance for ambiguity.

Up-transpile: weak to strong typing. Requires inference — we have to reconstruct type information the BRE never captured.

Every philosophical divide becomes a concrete engineering decision.

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Shipping It

We ship the MDH-flavored outcome.

Promises made to the BRE team:

"Try it for a release. If anyone complains, we add support back for the old way."

Later: partial convergence. The teams meet in the middle, mostly.

I get pulled away to work on another urgent project.