Module expr 

The closed expression set a workflow runs.

The schema generator parses every condition, set: value and {{ }} template of a workflow when it generates, refuses what is not in this set, and writes the result as the data types of this module (an Expr tree, a Template, a Tpl value). The engine evaluates them over the instance’s JSON context; nothing is parsed at run time.

What an expression can say:

• paths into context, event, result, error and config, with .key and [n], and steps.<name>.completed; a missing key reads as null;
• literals (null, booleans, numbers, strings, arrays) and duration literals (15m, 30d);
• == != < <= > >=, && || !, + - * / %, a ?? b, a ? b : c, a in [..];
• .length, .contains(x), .includes(x), .starts_with(x), .ends_with(x);
• now(), new_uuid(), coalesce(a, b, ..), len(x);
• a function the workflow declares under functions:, called through Funcs.

time + duration and time - duration add to an RFC 3339 text and answer one; < and friends compare two RFC 3339 texts as instants.

Structs

NoFuncs

A Funcs that declares nothing: every call is an error.

Scope

What an expression reads.

Template

A string with {{ }} holes. A template that is one hole renders as that expression’s own value (a number stays a number, an object stays an object); anything else renders as text.

Enums

BinOp

A binary operator.

Dur

A duration: fixed, or a template evaluated when it is needed ({{ context.minutes }}m).

Expr

A compiled expression.

Part

A piece of a template.

Root

Where a path starts.

Seg

One step of a path.

Tpl

A value of a step’s parameters: a literal, a template, or a map or list of them.

Traits

Funcs

The functions a workflow declares under functions:, implemented by hand.

Functions

canonical

The canonical text of a value as a wait key: strings as they are, null as null, a whole number without a fraction.

eval

Evaluate expr over scope.

holds

Evaluate expr and read the answer as a condition.

parse_duration

Read 30s, 15m, 24h, 7d, 2w, or a bare number of seconds, as seconds.

render

Render a parameter value.

render_duration

Render a duration: seconds, or a template read with parse_duration.

render_template

Render a template: one hole is that expression’s value, anything else is text.

text_of

The text of a value inside a larger template: strings as they are, null as nothing.

truthy

Whether v counts as true: not null, false, 0 or "".

wait_key

The key a wait is matched on: the canonical text of each value, in the order given, as a JSON array. Both the instance (from its context) and the event (from its payload) build it the same way, so equal values make equal keys.