Nodes and Edges

Node Types

merx has four types of nodes:

Start Node

The entry point of the program. Every program must have exactly one.

Start
Start([Start])
Start(["Start"])

End Node

The exit point of the program. Every program must have exactly one. No edges can go out from the End node.

End
End([End])
End(["End"])

Process Node

Executes one or more statements. Enclosed in square brackets []:

A[println 'hello']
A["println 'hello'"]

A Process node can have at most one outgoing edge.

Condition Node

Evaluates a condition and branches based on the result. Enclosed in curly braces {} with a trailing ?:

B{x > 0?}
B{"x > 0?"}

A Condition node must have exactly two outgoing edges labeled Yes and No.

Node IDs

Each node has a unique ID. IDs follow these rules:

• Must start with a letter (A-Z, a-z) or underscore (_)
• Can contain letters, digits (0-9), and underscores
• Start, End, true, false, input, as, int, str, println, print, error are reserved and cannot be used as node IDs or variable names

A           %% valid
myNode      %% valid
_count      %% valid
node123     %% valid

Edge Syntax

Basic Arrows

A --> B
A ---> B

You can add extra hyphens to make the arrow longer (--...->). This affects the diagram layout but not execution.

Edge Labels

Labels can be added in two ways:

Pipe syntax:

A -->|label| B

Inline syntax:

A -- label --> B

Both syntaxes produce the same result. You cannot use both on the same edge.

Condition Labels

Condition nodes require Yes and No labels (case-insensitive) on their outgoing edges:

flowchart TD
    Start --> A[x = 42]
    A --> B{x > 0?}
    B -->|Yes| C[println 'positive']
    B -->|No| D[println 'not positive']
    C --> End
    D --> End

Exit Codes

You can specify an exit code on edges that lead to the End node using the exit N syntax, where N is an integer from 0 to 255:

flowchart TD
    Start --> A[ok = false]
    A --> B{ok?}
    B -->|Yes| End
    B -->|No, exit 1| End

Exit code variants:

Label	Description
exit N	Exit with code N
Yes, exit N	Yes branch with exit code
No, exit N	No branch with exit code

If no exit code is specified, the default is 0.

WARNING

Exit codes can only be used on edges that point to the End node. Using them on other edges will cause a validation error.