isnow

A date/time pattern language for repetition. One compact expression describes anything from a fixed instant to a complex recurrence, and answers a single question: is it now?

An isnow (the language, and a pattern string in it) is a matcher, not a generator. */*/1 * 12:*:00 matches every instant on the first of a month during the noon hour; an implementation exposes is(isnow, instant) — the isnow holds at an instant when every field constraint is satisfied. It is a strict superset of cron in expressiveness — sets, spans, exclusions, from-end counting, steps, and since/until bounds, over one uniform per-field algebra. Every concept has a fixed name: see SPECIFICATION.md §0.

6                       every day at 06:00
M,W,F midnight          Mon/Wed/Fri at 00:00
11/ Th-[1] noon         last Thursday of November at noon
::+[9] >=6 <=18         every 9 seconds from 06:00 to 18:00
M-F-[1] noon            the last business day of the month at noon
+[90mn]                 every 90 minutes (a true interval, crossing hours)
M-F +[30mn] >=9 <=17    every 30 minutes, 9-to-5, on weekdays

This repository is the grammar-first home of the language: the ANTLR4 grammar is the source of truth, and every implementation is generated from it and verified against one shared corpus.

• Grammar: IsnowParser.g4 · IsnowLexer.g4
• Specification (terminology + semantics): SPECIFICATION.md
• Conformance corpus: conformance/ — 180 language-agnostic cases every implementation must pass. Validate with make corpus (no toolchain needed).
• Implementations: tsvsheet/go-isnow (the Go library), tsvsheet/isnow.go (the isnow CLI and HTTP server, built on it), and tsvsheet/isnow.js (the JS library + web playground).
• Generate a parser: make image && make go writes the Go parser into ../isnow.go/internal/isnowgrammar, make js into ../isnow.js/src/isnowgrammar; python/java/cpp land in gen/<lang>/ for future implementations. make help lists targets. The Java/ANTLR toolchain is isolated in Docker; nothing else is needed to regenerate.

Status: Draft 0.1.0 — recovered and consolidated from the original 2011 design.