Conditions

Conditions let Wist programs choose one of two result expressions.

Condition support is dialect-dependent. A program can use if only when the active dialect includes the modules that own condition syntax and the comparison or equality operators used by the condition expression.

When to read this page

Read this page when you want to write if / else expressions or when a custom dialect needs conditional logic.

Goal

Understand the current if syntax, result selection behavior and module dependencies.

Minimal if/else

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

Expected result:

1

If the condition is not satisfied, Wist returns the alternative expression:

if 2 == 3 (1) else (2)

Expected result:

2

Syntax shape

The current documented shape is:

if condition (thenExpression) else (elseExpression)

The result expressions are grouped with parentheses. Multi-line grouped expressions are possible when the selected modules support the required inner syntax.

Conditions with variables

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

Expected result:

10

This requires variable and identifier support in addition to condition and equality support.

Nested conditions

if 2 == 2 (
    if 3 == 3 (9) else (8)
) else (7)

Expected result:

9

Nested conditions are useful in tests because they prove that grouped conditional expressions are parsed and lowered consistently.

Required modules

Depending on the expression, a conditional dialect may need modules such as:

use Conditions,ComparisonConditions,Equality,BooleanConditions,Arithmetic,Numbers,Identifier,Variables,Scopes,Whitespaces

The exact set depends on the condition expression and result contents:

• Conditions owns conditional syntax.
• Equality is needed for ==-style equality checks.
• ComparisonConditions is needed for comparison operators such as <, <=, > or >=.
• BooleanConditions is needed for boolean composition when used.
• Variables and Identifier are needed when conditions read named values.

Conditions in formula DSLs

A pricing or scoring DSL may use conditions to express thresholds:

if price > 100 (price - 10) else (price)

This can be useful, but it also broadens the DSL surface. Add it only when conditional logic is part of the product requirement and test both outcomes.

What to test

For every dialect that enables conditions, test:

• satisfied condition result;
• unsatisfied condition result;
• variable-based conditions if variables are allowed;
• invalid condition syntax;
• compiler/interpreter parity when both backends are exposed.

Common mistakes

• Adding Conditions but forgetting equality or comparison modules required by the condition expression.
• Assuming if syntax works in minimal arithmetic dialects.
• Testing only one outcome.
• Documenting conditions as general statement syntax when the examples use expression-like result values.
• Letting compiler and interpreter disagree on nested condition lowering.

Next

Continue with Loops for repeated execution.