Syntax Tour

This page is a tour, not a full language reference. It shows small Wist snippets that are useful when learning the reference language and when deciding which modules a dialect should include.

When to read this page

Read this after First Program and Mental Model.

Goal

Understand the basic Wist syntax surface used by shipped dialect examples: numbers, arithmetic, variables, conditions, loops and scopes.

Prerequisites

• You can run Wistc from the repository root.
• You understand that syntax exists only when the active dialect includes the owning module.

Steps

1. Numbers and arithmetic

2 + 3 * 4

Expected result:

14

Arithmetic precedence follows the normal order: multiplication and division bind before addition and subtraction. Parentheses can be used to group expressions:

(2 + 3) * 4

2. Variables

Variables are declared with let and can be updated later:

let x = 2
let y = 3
x = x + y
x

This uses the Variables, Identifier, Numbers, Arithmetic, Scopes and Whitespaces modules.

3. Conditions

A simple if/else expression:

if 2 == 2 (1) else (2)

Expected result:

1

A condition with a variable:

let x = 2
if x == 2 (10) else (20)

This requires condition, comparison, equality, variable and identifier support. In shipped full dialects, these are provided by modules such as Conditions, ComparisonConditions, Equality, Variables and Identifier.

4. Loops

A while loop:

let sum = 0
let i = 1

while i <= 5 (
    sum = sum + i
    i = i + 1
)

sum

Expected result:

15

For while, the condition can be written without parentheses when it parses as one expression node. Parentheses are still allowed for readability. Multi-operation loop bodies should remain grouped.

Loops require the Loops module plus variables, comparison and arithmetic support.

5. for loops

The shipped full-default example uses this form:

let sum = 0

for (let i = 1) (i <= 5) (i = i + 1) (
    sum = sum + i
)

sum

Expected result:

15

Use this example as the canonical reference for current for syntax. The current for parser expects initialization, condition, update and body to be grouped.

6. Comments

When the Comments module is selected, single-line and block comments are allowed:

// single-line comment
let x = 2
/* block
   comment */
x + 5

Expected result:

7

7. Interop expression in full dialects

The full dialect can run C# interop expressions when CSharpInterop and trusted capabilities are enabled:

NumbersModule.Core.RealNumberImpl.Add(2, 5)

Expected result:

7

Do not use this in restricted dialects. Interop is intentionally excluded from examples such as composition-restricted.

Expected result

You should be able to map each syntax feature to the module that owns it. If a snippet fails under a custom dialect, check whether that dialect includes the required modules.

What happened internally

Each syntax feature is introduced by one or more modules. Modules register lexer rules, parser node creators and AST-to-bytecode visitors. Dialects decide which modules are visible to the runtime.

Common mistakes

• Trying to use variables in a dialect that omits Variables or Identifier.
• Trying to use loops in a dialect that omits Loops.
• Treating the parenthesized while condition examples as the only valid form.
• Using cil mode with a dialect that only exposes interpreter.
• Assuming restricted dialects are hardened sandboxes. They constrain composition, but process isolation is still required for untrusted execution.

Next

Continue with Dialect Files.