Function infer_type 

pub fn infer_type<S: BuildHasher>(
    expr: &Expr,
    env: &HashMap<Arc<str>, ExprType, S>,
) -> Result<ExprType, TypeError>

Infer the output type of an expression given input variable types.

This performs a single pass over the expression tree, using builtin signatures where available and falling back to ExprType::Any for polymorphic or opaque constructs.

Errors

Returns TypeError::UnboundVariable if a variable is not in the environment.