Control Flow

Programs often need to choose between actions, repeat work, or recover when an operation fails. Control flow defines those decisions and the order in which statements run. For example, a program can process every invoice but stop when a required value is missing.

Devlish groups statements with indentation. The examples below explain conditions, loops, and error recovery; read Syntax Basics first if comparisons and assignment are new to you.

If / Otherwise

Branch execution based on a condition. The Otherwise block runs when the condition is false.

If score > 70:
  Print "passed"
  Set status to "approved"
Otherwise:
  Print "failed"
  Set status to "rejected"

Conditions support comparisons and boolean operators:

If status equals "active" and balance > 0:
  Print "eligible"

For Each Loop

Iterate over a list. The loop variable is available inside the block.

statuses equals list of "pending", "active", and "closed"

For each status in statuses:
  Print status

Iterating over records from a list:

For each invoice in invoices:
  Print amount of invoice

While Loop

Repeat while a condition is true.

retry_count equals 0

While retry_count is less than 3:
  retry_count equals retry_count plus 1
  Print retry_count

Until Loop

Repeat until a condition becomes true (inverse of While).

status equals "pending"

Until status is "complete":
  # do work
  status equals "complete"

Continue and Break

Continue skips to the next iteration. Break exits the loop entirely.

For each item in items:
  If status of item equals "skip":
    Continue
  If priority of item equals "urgent":
    Print item
    Break

Try / Otherwise (Error Recovery)

Wrap risky operations in Try. If an error occurs, execution jumps to Otherwise and the error is stored in last_error.

Try:
  Read JSON from "config.json" as config
Otherwise:
  config equals record with "default" as mode
  Print last_error

Try blocks catch validation failures, file errors, HTTP errors, and explicit Fail with statements.

Fail With

Stop execution with an error message.

Fail with "Contact email is required"

When combined with Require:

Require review_status is "approved" otherwise fail with "Review must be approved"

If Fail with receives a record, it serializes as structured JSON:

Fail with record with "missing_field" as code and "Email required" as message

Nesting

Control flow blocks can nest freely:

For each project in projects:
  If status of project equals "active":
    Try:
      amount equals value of project
      amount must be at least 10000
    Otherwise:
      Print "Validation failed for project"
      Continue