Creating Boolean Expressions

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Creating Expressions Using Built-in Constructors

Creating a BoolExpr object is pretty straightforward.

do
    local function FilterExpression1()
        if <...> then
            return true
        end
        return false
    end

    local function FilterExpression2()
        if <...> then
            return true
        end
        return false
    end

    do
        -- Create a new boolean expression
        local and_expr = BoolExpr.And(FilterExpression1, FilterExpression2)

        ...
    end
end

The BoolExpr.And() constructor has a built-in check against nil arguments.

Manually Constructed Boolean Expressions

It is also possible to create boolean expressions using ordinary tables, by using the boolean expression operators declared as enum types.

do
    local function FilterExpression1()
        if <...> then
            return true
        end
        return false
    end

    local function FilterExpression2()
        if <...> then
            return true
        end
        return false
    end

    do
        -- Create a new boolean expression
        local and_expr = {BoolExpr.AND, FilterExpression1, FilterExpression2}

        ...
    end
end

In this particular case, the BoolExpr.AND boolean expression operator is used (see Boolean Expression Operators). The user have the full responsibility of ensuring the validity (i.e., not nil) of the passed expressions when using this method of construction since it does not have the built-in checking and assertion, though consequently, this method has no additional overhead whatsoever as the process is just a simple table creation.

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Next: Evaluating Boolean Expressions

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