10x Faster Mobile App Dev with PureScript Presto. 

● Built large scale systems at Juspay, Amazon, Trilogy serving millions of users ● A convert to PureScript from Clojure / JavaScript ● Passionate about building Creation tools Hello! I’m Vimal Kumar, CEO of Juspay 

Why do commercial apps take months to develop and millions of $$ to maintain? PROBLEM 

Why are Apps hard? Unnatural programming model for Business Logic ● Event based model complicates transactional apps ● No clarity of flow of control - too many jumps ● Can’t compose flows, smaller to larger, due to async nature 

Why are Apps hard? Frameworks focus on Getting started quick; Not on fundamentals to Control complexity ● Complexity of serious apps is exponentially increasing. ● Need a strong theory like Functional Programming / Category theory with extreme focus on composition. ● Hard theories need years of investment to get practical advantage. 

Why are Apps hard? Fragmented Architecture, Need Unification ● Frontend, Backend, Persistence, External service integration, Analytics, Business Logic, Infrastructure. ● All are handled in different ways. They can be unified with a few simple building blocks. 

Presto’s vision is to enable Freshers/PMs build and maintain apps with 10x less time and effort. It needn’t be this way! 

How? ● Conversational UX DSL ● Business Flows as Goal Trees ● PureScript - Pure FP, Category Theory ● Unify, Only 3 Blocks, UI | Flows | Data 

UX Flows as Conversational DSL User System App Welcome Tell Ask Ask-Options Ask-Search Ask-Confirm Thank Delight Suggest Cross Sell Notify Fetch Detect Search Commit Track SetTimer Etc.. App The App Weaves a. Conversation between User & System towards a Goal Goal 

Business Logic as Goal Trees ● Composable Goals! ● Understandable to non-tech - Designers, Product Managers Introduce Verify Mobile Create VPA Goal: BHIM Onboarding UI: Step 1 Help UI: Step 2 Help UI: Success OR Verify Mobile With OTP Verify Mobile Sending SMS API: Trigger OTP Poll SMS Inbox for OTP More steps Tree extends here… Local API: Send SMS Code Poll Server for SMS Code UI: Success More steps Tree extends here… More steps Tree extends here… UI: Welcome UI: Ask Mobile 

Welcome Dilip to the app Ask to pay the DTH bill (why not give some incentive!) > Ask to choose DTH Operator. If a lot, let him search > Ask for his Customer ID. Show HELP on where to find the Customer ID > Fetch his Customer Name and latest due bill amount :: LOAD > Show the bill details and Ask to pay SubFlow Collect_UPI_MPIN Commit the payment and Show confirmation status. Cross Sell Ask if he’d like to set up Auto-deduct OR Payment reminder for future bills > Thank Dilip. Goal Tree as a Narrative 

DSL Goal Tree - Code Walkthrough 

PureScript - Pure FP ● Composition, State Management, Conciseness and Clarity ● CPS (Continuation passing style) for the DSL Goal Trees ● Choice of PureScript - Best of Haskell and JavaScript. ● Category Theory - Functors / Monads / Applicatives 

Just 3 Building Blocks - Unify ● UI Structure - Visual Components like React ● Goal Tree - Flows as Pure Functions ○ Represents the entire business logic ○ Unified Backend and Frontend ● Data as Types ○ Single set of types for Frontend, Backend, UI, Storage ○ Types mapped to DB data model 

Why PureScript and CPS? LANGUAGE OPTIONS ARCHITECTURE OPTIONS PureScript GhcJS ClojureScript Haskell Like + Strong FP - Focus on Purity, Composition, Concise. + Types - Few errors, Easy refactoring JS Integration + Solid and easy JS FFI + JS Code Small & Reliable - New and evolving + Implements all Haskell’s features and access to most Haskell Libraries. - Large size JS and not so reliable runtime + Is a Lisp! + Strong Developer community + Proven runtime - Lacks Types - Lacks strong math / category theory foundation of Haskell CPS (Continuation Passing) Elm Architecture / Redux Pure FRP Maps directly to UX flows / flows as conversion funnel. Global state complicates transactional flows vs CPS manages local state in stack More general than CPS but complicates UX flows. Presto will add FRP support in future 

How is this 10X? ● Reuse of Lego Blocks: UI / Flow / Data components become extremely reusable across apps as we use Pure FP techniques. ● FP and Types guarantee Reliability for Free, minimizes testing. ● The DSL - Unifies Product / Dev and Design teams, improves clarity & removes communication overhead. ● Unified UI code for Android / iOS / Progressive Webapp / Desktop Web removes necessity for multiple UI dev teams ● Unified frontend / backend removes need for separate mobile and backend teams 

Apps in Production UPI SDK for top Apps UPI for Petroleum New Juspay Safe Potential for 100M+ users 

Next Steps School of Functional Programming 

Next Steps Visual Programming ● Auto generate UI components from design - Sketch plugin ● UX Goal Tree as an editable Fishbone diagram 

Thanks! Want to contribute? Just mail us at [email protected]