effect<= ( effect1 effect2 -- ? )
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Vocabulary
effects

Inputs

effect1	an effect
effect2	an effect

Outputs

?

a boolean

Word description
Tests if effect1 is substitutable for effect2. What this means is that both stack effects change the stack height by the same amount, the first takes a smaller or equal number of inputs as the second, and either both or neither one terminate execution by throwing an error.

Definition

USING: accessors combinators kernel math sequences ;

IN: effects

: effect<= ( effect1 effect2 -- ? )
    {
        { [ over terminated?>> ] [ t ] }
        { [ dup terminated?>> ] [ f ] }
        { [ 2dup [ bivariable-effect? ] either? ] [ f ] }
        {
            [
                2dup
                [ variable-effect? ] [ variable-effect? not ]
                bi* and
            ]
            [ f ]
        }
        { [ 2dup [ in>> length ] bi@ > ] [ f ] }
        { [ 2dup [ effect-height ] same? not ] [ f ] }
        [ t ]
    } cond 2nip ; inline