prelude: input builtin - #19
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Python's input(prompt) name-for-name, the io effect coming in to pair with print's going out; `input "n? " |> String.toInt` is the idiomatic total parse. Monomorphic, seeded next to print; arity rides PRELUDE so lowering and completion need nothing new. DESIGN documents the environment caveats (REPL worker protocol owns stdin; the Pyodide playground cannot block on stdin - pyfun run and Jupyter are the home turf).
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simontreanor
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Jul 31, 2026
Two user-visible additions since 0.2.0 -- the `input` prelude builtin
(`string ->{io} string`, #19) and caller-supplied `extern` keyword slots
(`kw = ...`, #21) -- plus five fixes, four of them from the first program
written in Pyfun in anger:
* imported schemes reused the exporting module's type-variable ids, silently
blocking generalization in the importing module and cascading to its
consumers (#26 / #27)
* a recursive function of arity >= 2 could not perform any effect -- the shape
of every loop in a language with no `while` (#24 / #28)
* a module that only matched an imported `Option` emitted `None_` without
importing it (#25 / #29)
* user identifiers collided with Python keywords, builtins the emitter calls,
and modules an `extern` imports (#23 / #30)
* the local-binder module-alias shadowing residual (#18)
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Adds
input : string ->{io} stringto the unqualified prelude - Python''sinput(prompt)name-for-name (input ""for promptless), the io effect coming in to pair withprint''s going out.input "n? " |> String.toInt : Option intis the idiomatic total parse, which should make for good lesson material later.One PRELUDE entry + one seeded scheme; arity registration, lowering, and LSP completion all ride the existing PRELUDE table. DESIGN.md documents the environment caveats: the REPL''s worker protocol owns stdin (the already-documented hazard), and the Pyodide playground cannot block on stdin -
pyfun runscripts and Jupyter are the home turf.Tests: typecheck (type, io-effect flow into
let purerejection, prompt must be a string), lowering shape (input("who? ")), an e2e that pipes a real stdin line through the emitted program, and a roundtrip entry. Full suite green; clippy clean.