Migrating to Rad v0.7¶

Version 0.7 introduces a breaking change to for-loop syntax. This guide will help you update your scripts.

Breaking Change: For-Loop Index Syntax¶

What Changed¶

The old implicit index syntax—where adding a second variable would make the first variable the index—has been removed. This syntax was confusing because adding a variable changed the meaning of existing variables.

Old Syntax (No Longer Works)¶

// This no longer works:
for idx, item in items:
    print(idx, item)

// Also broken:
for i, name, age in zip(names, ages):
    print(i, name, age)

New Syntax¶

Use the with <identifier> clause to access loop context:

// New way to access index:
for item in items with loop:
    print(loop.idx, item)

// With zip:
for name, age in zip(names, ages) with loop:
    print(loop.idx, name, age)

The context object provides:

loop.idx - Current iteration index (0-based)
loop.src - Immutable snapshot of the original collection

Migration Steps¶

Find all for-loops with two or more variables
Determine if the first variable is an index
If yes → use the with loop syntax
If no (it's unpacking nested lists) → no change needed
Update the syntax

Example 1: Simple Index Access¶

// Before
for idx, name in names:
    print(idx, name)

// After
for name in names with loop:
    print(loop.idx, name)

Example 2: With zip¶

// Before
for idx, name, age in zip(names, ages):
    print(idx, name, age)

// After
for name, age in zip(names, ages) with loop:
    print(loop.idx, name, age)

Example 3: Unpacking (No Change Needed)¶

// This still works - unpacking nested lists
pairs = [["a", 1], ["b", 2]]
for letter, number in pairs:
    print(letter, number)

// Can add context if you want the index too
for letter, number in pairs with loop:
    print(loop.idx, letter, number)

Example 4: Map Iteration¶

// Before (if you had this pattern)
for idx, key in myMap:
    print(idx, key)

// After
for key in myMap with loop:
    print(loop.idx, key)

// Key-value iteration is unchanged
for key, value in myMap:
    print(key, value)

// With context
for key, value in myMap with loop:
    print(loop.idx, key, value)

Error Messages¶

If Rad detects you might be using the old syntax, it will show a helpful error:

Error: Cannot unpack 'int' into 2 values

Note: The for-loop syntax changed. It looks like you may be using the old syntax.
Old: for idx, item in items:
New: for item in items with loop:
         print(loop.idx, item)

Why This Change?¶

The old syntax had several problems:

Confusing: Adding a variable changed the meaning of the first variable
Inconsistent: Didn't work well with zip() and unpacking
Error-prone: Easy to accidentally shift variable meanings

The new syntax is explicit, consistent, and works the same way in all contexts.

Bonus: Rad Block Lambda Context¶

As part of this release, rad block map and filter lambdas can now accept an optional context parameter:

Population:
    map fn(p, ctx) "{p / sum(ctx.src) * 100:.1}%"

The context provides:

ctx.idx - Current row index
ctx.src - Full column data (immutable snapshot)
ctx.field - Field name being transformed

See the Rad Blocks guide for details.