Shoelace formula for polygonal area: Difference between revisions

=={{header|Lambdatalk}}==

<lang scheme>

{def shoelace

{lambda {:pol}

{abs

{/

{-

{+ {S.map {{lambda {:pol :i} {* {car {A.get :i :pol}}

{cdr {A.get {+ :i 1} :pol}}}} :pol}

{S.serie 0 {- {A.length :pol} 2}}}

{* {car {A.get {- {A.length :pol} 1} :pol}}

{cdr {A.get 0 :pol}}}}

{+ {S.map {{lambda {:pol :i} {* {car {A.get {+ :i 1} :pol}}

{cdr {A.get :i :pol}}}} :pol}

{S.serie 0 {- {A.length :pol} 2}}}

{* {car {A.get 0 :pol}}

{cdr {A.get {- {A.length :pol} 1} :pol}}}}} 2}}}}

-> shoelace

{def pol

{A.new {cons 3 4}

{cons 5 11}

{cons 12 8}

{cons 9 5}

{cons 5 6}}}

-> pol = [(3 4),(5 11),(12 8),(9 5),(5 6)]

{shoelace {pol}}

-> 30

</lang>