81 lines
2.6 KiB
Markdown
81 lines
2.6 KiB
Markdown
# Flow Blocks and Arrow Piping (Design Draft)
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Status: design-only during the feature‑pause (no implementation)
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Goal
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- Make control/data flow visually obvious while keeping the core minimal.
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- Core = anonymous `{ ... }` blocks + `->` chaining with `_` or `|args|` as the input placeholder.
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- Always desugar to plain sequential let/if/call; zero new runtime constructs.
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Core Syntax
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- Serial (value flow):
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```nyash
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{ readConfig() }
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-> { |cfg| validate(cfg) }
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-> { |cfg| normalize(cfg) }
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-> { |cfg| save(cfg) }
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```
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- Placeholder short form:
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```nyash
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{ fetch() } -> { process(_) } -> { output(_) }
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```
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- If/Else with horizontal flow:
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```nyash
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if cond -> { doA() } else -> { doB() }
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```
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Semantics
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- `{ ... }` is an anonymous scope usable as expression or statement.
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- `->` passes the left result as the first parameter of the right block.
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- Left returns `Void` → right cannot use `_`/`|x|` (compile-time error in MVP spec).
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- `_` and `|x,...|` are exclusive; mixing is an error.
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Lowering (always zero-cost sugar)
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- Chain desugars to temporaries and calls:
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```nyash
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# {A} -> { |x| B(x) } -> { |y| C(y) }
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t0 = A();
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t1 = B(t0);
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t2 = C(t1);
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```
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- If/Else chain desugars to standard if/else blocks; merges follow normal PHI wiring rules.
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Match normalization via guard chains
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- Prefer a single readable form:
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```nyash
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guard cond1 -> { A }
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guard cond2 -> { B }
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else -> { C }
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```
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- Lowers to first-match if/else chain. No new pattern engine is introduced.
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Range and CharClass guards (design)
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- Range: `guard ch in '0'..'9' -> { ... }` → `('0' <= ch && ch <= '9')`.
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- CharClass: `guard ch in Digit -> { ... }` → expands to ranges (e.g., '0'..'9').
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- Multiple ranges combine with OR.
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Formatting (nyfmt guidance)
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- Align arrows vertically; one step per line:
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```
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{ fetch() }
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-> { validate(_) }
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-> { save(_) }
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```
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- Suggest factoring when chains exceed N steps; prefer naming a scope helper.
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Observability (design only)
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- `NYASH_FLOW_TRACE=1` prints the desugared steps (`t0=...; t1=...;`).
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Constraints (MVP)
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- No new closures; anonymous blocks inline when capture-free.
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- Recursion not required; focus on linear/branching chains.
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- ASI: treat `->` as a low-precedence line-continue operator.
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Tests (syntax-only smokes; design)
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- flow_linear: `read→validate→save` matches expected value.
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- flow_placeholder: `{f()} -> { process(_) } -> { out(_) }`.
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- flow_if: `if cond -> {A} else -> {B}` behaves like standard if.
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Pause note
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- Documentation and design intent only. Implementation is deferred until after the feature‑pause (post‑bootstrap).
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