# SPDX-License-Identifier: Apache-2.0
# yaml-language-server: $schema=https://nika.sh/spec/v1/workflow.schema.json
#
# 02 · Parallel fan-out + merge — the core DAG pattern.
#
# You never write "run these in parallel". You write what each task NEEDS,
# and the shape of the graph falls out: three tasks that need nothing from
# each other are three tasks the engine may run at once. Concurrency is a
# consequence of the dependencies, not an instruction.
#
# Demonstrates ·
#   - implicit parallelism · no deps between three tasks → one wave, run together
#   - `const:` · a fixed value baked into the file, never caller-supplied
#   - `with:` value edges · what a task binds is what it waits for
#   - `${{ tasks.<id>.output }}` · reading an upstream result
#
# DAG shape ·   angle ─┐
#               cost  ─┼─→ synthesize
#               risk  ─┘
#
# Run · nika run examples/02-parallel-fanout.nika.yaml

nika: v1
workflow:
  id: parallel-fanout

# The dry twin, on purpose: this file teaches SHAPE, and the twin makes the
# shape visible — it echoes each prompt back, so `synthesize`'s output shows
# the three upstream answers arriving inside it. Swap in any real model
# (`--model ollama/qwen3.5:4b`) and only the prose changes, never the graph.
model: mock/echo

permits: {}   # pure compute · no file, no host, no program (see 01)

const:
  topic: "adopting Rust for a backend rewrite"

tasks:
  # No task below names another, so the engine puts all three in wave 1 and
  # runs them concurrently. `nika check` prints the waves it derived — read
  # that plan before you reach for a knob to make something parallel.
  angle:
    infer:
      prompt: "Give the strategic angle on · ${{ const.topic }}"
      max_tokens: 512

  cost:
    infer:
      prompt: "Give the cost angle on · ${{ const.topic }}"
      max_tokens: 512

  risk:
    infer:
      prompt: "Give the risk angle on · ${{ const.topic }}"
      max_tokens: 512

  # The merge. `with:` does two jobs at once: it aliases the upstream outputs
  # to short local names, and — because a binding IS a dependency — it is what
  # puts this task in wave 2. Bind three tasks, wait for three tasks.
  synthesize:
    with:
      a: ${{ tasks.angle.output }}
      c: ${{ tasks.cost.output }}
      r: ${{ tasks.risk.output }}
    infer:
      prompt: |
        Synthesize one recommendation from three analyses.
        Strategy · ${{ with.a }}
        Cost · ${{ with.c }}
        Risk · ${{ with.r }}
      max_tokens: 1024

# The return value · read it with `--output json` (see 01).
outputs:
  recommendation: ${{ tasks.synthesize.output }}

the path · 02

Parallel fan-out + merge — the core DAG pattern.

run itnika try 02-parallel-fanout

02-parallel-fanout.nika.yaml

1# SPDX-License-Identifier: Apache-2.02# yaml-language-server: $schema=https://nika.sh/spec/v1/workflow.schema.json3#4# 02 · Parallel fan-out + merge — the core DAG pattern.5#6# You never write "run these in parallel". You write what each task NEEDS,7# and the shape of the graph falls out: three tasks that need nothing from8# each other are three tasks the engine may run at once. Concurrency is a9# consequence of the dependencies, not an instruction.10#11# Demonstrates ·12#   - implicit parallelism · no deps between three tasks → one wave, run together13#   - `const:` · a fixed value baked into the file, never caller-supplied14#   - `with:` value edges · what a task binds is what it waits for15#   - `${{ tasks.<id>.output }}` · reading an upstream result16#17# DAG shape ·   angle ─┐18#               cost  ─┼─→ synthesize19#               risk  ─┘20#21# Run · nika run examples/02-parallel-fanout.nika.yaml2223nika: v124workflow:25  id: parallel-fanout2627# The dry twin, on purpose: this file teaches SHAPE, and the twin makes the28# shape visible — it echoes each prompt back, so `synthesize`'s output shows29# the three upstream answers arriving inside it. Swap in any real model30# (`--model ollama/qwen3.5:4b`) and only the prose changes, never the graph.31model: mock/echo3233⛨permits: {}   # pure compute · no file, no host, no program (see 01)3435const:36  topic: "adopting Rust for a backend rewrite"3738tasks:39  # No task below names another, so the engine puts all three in wave 1 and40  # runs them concurrently. `nika check` prints the waves it derived — read41  # that plan before you reach for a knob to make something parallel.42  angle:43    ◇infer:44      prompt: "Give the strategic angle on · ${{ const.topic }}"45      max_tokens: 5124647  cost:48    ◇infer:49      prompt: "Give the cost angle on · ${{ const.topic }}"50      max_tokens: 5125152  risk:53    ◇infer:54      prompt: "Give the risk angle on · ${{ const.topic }}"55      max_tokens: 5125657  # The merge. `with:` does two jobs at once: it aliases the upstream outputs58  # to short local names, and — because a binding IS a dependency — it is what59  # puts this task in wave 2. Bind three tasks, wait for three tasks.60  synthesize:61    with:62      a: ${{ tasks.angle.output }}63      c: ${{ tasks.cost.output }}64      r: ${{ tasks.risk.output }}65    ◇infer:66      prompt: |67        Synthesize one recommendation from three analyses.68        Strategy · ${{ with.a }}69        Cost · ${{ with.c }}70        Risk · ${{ with.r }}71      max_tokens: 10247273# The return value · read it with `--output json` (see 01).74outputs:75  recommendation: ${{ tasks.synthesize.output }}76

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