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69a203c2a8
Allows literal $ signs in prompts and DOT files by writing $$. Also refactors VariableExpansionTransform to use expand_vars instead of string replace, fixing a substring-matching bug with $goal. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
76 lines
2.4 KiB
Text
76 lines
2.4 KiB
Text
---
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title: "Variables"
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description: "Using variables in workflows"
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---
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Arc supports `$variable` placeholders that let you parameterize workflows without editing the DOT file.
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## Run config variables
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Define variables in the `[vars]` section of a run config TOML file:
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```toml
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version = 1
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goal = "Run tests for $repo_name"
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graph = "check.dot"
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[vars]
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repo_name = "arc"
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repo_url = "https://github.com/qltysh/arc"
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language = "rust"
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```
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These variables are expanded into the DOT source **before** the graph is parsed. You can use `$variable` anywhere in the DOT file — goals, prompts, labels, scripts, or any other attribute:
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```dot title="check.dot"
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digraph Check {
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graph [goal="Run tests for $repo_name"]
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start [shape=Mdiamond, label="Start"]
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exit [shape=Msquare, label="Exit"]
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clone [label="Clone", shape=parallelogram, script="git clone $repo_url repo"]
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test [label="Test", prompt="Run the $language test suite in the repo/ directory."]
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start -> clone -> test -> exit
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}
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```
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When launched with `arc run start run.toml`, Arc replaces `$repo_name`, `$repo_url`, and `$language` with their values before parsing the graph.
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### Undefined variables
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If a `$variable` in the DOT file has no matching entry in `[vars]`, Arc raises an error. This catches typos early — a misspelled `$langauge` fails immediately rather than passing a literal `$langauge` to the LLM.
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### Escaping `$`
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To include a literal `$` in the output, write `$$`:
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```dot
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test [prompt="The env var is $$HOME"]
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```
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This produces `The env var is $HOME` without treating `$HOME` as a variable reference. A bare `$` not followed by an identifier character (e.g. `costs $5`) does not need escaping.
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## The `$goal` variable
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Inside agent and prompt node prompts, Arc automatically expands `$goal` to the workflow's `goal` attribute. This happens at runtime, after graph parsing:
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```dot title="example.dot"
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digraph Example {
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graph [goal="Implement the login feature"]
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plan [label="Plan", prompt="Create a plan for: $goal"]
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}
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```
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The plan node's prompt becomes `"Create a plan for: Implement the login feature"`.
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## Variable merging
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When using server-level run defaults alongside a run config TOML, variables are merged. Task config vars override default vars when keys collide:
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| Source | Priority |
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|---|---|
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| Run config TOML `[vars]` | Highest — wins on collision |
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| Server defaults `[vars]` | Lowest — provides fallback values |
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