Evaluate Expressions Only
========================

{{#include ../links.md}}

Sometimes a use case does not require a full-blown scripting _language_, but only needs to evaluate _expressions_.

In these cases, use the `Engine::compile_expression` and `Engine::eval_expression` methods or their `_with_scope` variants.

```rust
let result = engine.eval_expression::<i64>("2 + (10 + 10) * 2")?;
```

When evaluating _expressions_, no full-blown statement (e.g. `if`, `while`, `for`) - not even variable assignment -
is supported and will be considered parse errors when encountered.

```rust
// The following are all syntax errors because the script is not an expression.

engine.eval_expression::<()>("x = 42")?;

let ast = engine.compile_expression("let x = 42")?;

let result = engine.eval_expression_with_scope::<i64>(&mut scope, "if x { 42 } else { 123 }")?;
```