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WalkLang Migration Guide

v1.8 to v1.9

v1.9 adds string interpolation for simple display text. Existing v1.8 source should not need changes.

New code can put display expressions inside single-quoted strings:

imp: string

var: word = 'paddle'
var: wordLength = string.len(word)
out: 'the secret word is {wordLength} characters long'

Interpolation accepts int, float, bool, string, and nullable string values. Use doubled braces when the output should contain literal braces:

out: '{{word}}'

v1.7 to v1.8

v1.8 adds stable helpers for simple terminal games and other string/array-heavy programs. Existing v1.7 source should not need changes.

New code can index strings by zero-based byte position:

out: 'walk'[1]

The string, array, and random modules add small helpers:

imp: string
imp: array
imp: random

var: guessed array[string] = []
var: words = ['dog', 'cat']
guessed = array.push(guessed, 'w')

out: string.contains('walk', 'al')
out: string.concat('walk', 'lang')
out: array.contains(guessed, 'w')
out: random.choice(words)

array.push returns a new array. Assign it back when the program should keep the appended value.

v1.6 to v1.7

v1.7 adds the stable in: expression for required-line stdin input. Existing v1.6 source should not need changes.

New code can read one line from stdin:

var: name = in:

Use an optional string prompt when interactive programs need one:

var: name = in: 'Name? '

in: returns string, strips the final line ending, preserves other whitespace, and runtime-stops if stdin reaches EOF before any text is read. It does not add typed input helpers such as in-int:.

v1.5 to v1.6

v1.6 adds local function type inference. Existing v1.5 source should not need changes.

Typed function signatures remain valid:

func: add(a int, b int) int
    return: + a b

New code may omit parameter and return types when the function body proves the types clearly:

func: power_four(n)
    return: ^ n 4

Ambiguous helper functions still need annotations. WalkLang does not infer ordinary function signatures from later call sites:

func: identity(value int)
    return: value

v2.1 to v2.2

v2.2 adds experimental simple generic functions. Existing v2.1 source should not need changes.

Recommended upgrade check:

walk version
walk check --warnings=error <entry.walk>
walk test <tests.walk>
walk build <entry.walk> -o build/app

For projects:

walk check --warnings=error
walk test
walk build

What Changed In v2.2

  • Generic function declarations are accepted, such as func: first[T](items array[T]) T.
  • Generic calls infer type arguments from ordinary call arguments.
  • Generic functions can compose with arrays, structs, methods, and user-module exports.
  • Generated C specializes concrete generic calls into predictable ordinary functions.

What Is Still Future

Traits, interfaces, generic structs, generic methods, explicit type-argument calls, and named-field constructors are not part of v2.2.

v1.5 to v2.0

v2.0 adds experimental structs and reserves the struct keyword.

Recommended upgrade check:

walk version
walk check --warnings=error <entry.walk>
walk test <tests.walk>
walk build <entry.walk> -o build/app

For projects:

walk check --warnings=error
walk test
walk build

What Changed In v2.0

  • struct: declarations compile.
  • Struct values can be constructed, read through dot fields, and assigned through mutable fields.
  • Structs work as function parameters, return values, array elements, and values returned by module functions.
  • User modules may contain top-level struct: declarations.

Breaking Change In v2.0

struct is now reserved. Rename any user-defined variable, function, field, or expression name called struct.

Named-field constructors, methods, traits, interfaces, and generic structs are not part of v2.0.

v1.4 to v1.5

v1.5 is a compatibility release-preparation pass. Stable v1.4 code should not need source changes.

Recommended upgrade check:

walk version
walk check --warnings=error <entry.walk>
walk test <tests.walk>
walk build <entry.walk> -o build/app

For projects:

walk check --warnings=error
walk test
walk build

What Changed

  • Compatibility policy is now explicit.
  • Release notes, install instructions, and deprecation policy are now documented.
  • Stable v1 behavior has a dedicated compatibility test suite.

What Did Not Change

  • No stable syntax was removed.
  • No stable standard-library API was removed.
  • No stable diagnostic category was removed.
  • No project-mode command was removed.

Stable Versus Draft

Before depending on a feature, check:

docs/SPEC.md
docs/SYNTAX.md
docs/STDLIB.md
docs/ERRORS.md
docs/COMPATIBILITY.md

If a feature is accepted by the compiler but absent from those docs and the compatibility tests, treat it as experimental.

Breaking Changes

Breaking changes to stable v1 behavior require one of these:

a v2.0.0 language boundary
a documented safety or correctness fix
proof that the behavior was never part of the stable v1 surface

When a documented safety fix breaks stable code, release notes must name the break and this guide must describe the migration.