Source code in the lambdatalk programming language

{def line_intersect
 {def line_intersect.sub
  {lambda {:111 :121 :112 :122 :211 :221 :212 :222}
   {let { {:x :111} {:y :121} 
          {:z {- {* {- :222 :221} {- :112 :111}}
                 {* {- :212 :211} {- :122 :121}} } }
          {:a {- :112 :111}} {:b {- :122 :121}}
          {:c {- :212 :211}} {:d {- :222 :221}}
          {:e {- :121 :221}} {:f {- :111 :211}}
          {:g {- :121 :211}} {:h {- :122 :121}}
        } {if {> :z 0}
           then {A.new ∞ ∞}
           else {let { {:x :x} {:y :y} {:a :a} {:b :b}
                       {:t1 {/ {- {* :c :e} {* :d :f}} :z} }
                       {:t2 {/ {- {* :a :g} {* :h :f}} :z} }
                } {if {and {>= :t1 0} {<= :t1 1} {>= :t2 0} {<= :t2 1}}
                   then {A.new {+ :x {* :t1 :a}} {+ :y {* :t1 :b}} }
                   else {A.new ∞ ∞}} }}}}}
 {lambda {:1 :2}
  {line_intersect.sub 
   {A.first {A.first :1}} {A.last {A.first :1}}     
   {A.first {A.last  :1}} {A.last {A.last  :1}}     
   {A.first {A.first :2}} {A.last {A.first :2}}     
   {A.first {A.last  :2}} {A.last {A.last  :2}} }}} 
-> line_intersect 

{line_intersect {A.new {A.new 4 0} {A.new 6 10}}
                {A.new {A.new 0 3} {A.new 10 7}}}
-> [5,5]
{line_intersect {A.new {A.new 4 0} {A.new 6 10}}
                {A.new {A.new 0 3} {A.new 10 7.1}}}
-> [5.010893246187364,5.05446623093682]
{line_intersect {A.new {A.new 1 -1} {A.new 4 4}}
                {A.new {A.new 2 5} {A.new 3 -2}}}
-> [2.5,1.5]
{line_intersect {A.new {A.new 0 0} {A.new 0 0}}
                {A.new {A.new 0 3} {A.new 10 7}}}
-> [∞,∞]
{line_intersect {A.new {A.new 0 0} {A.new 1 1}}
                {A.new {A.new 1 2} {A.new 4 5}}}
-> [∞,∞]