to basic make "linenumbers [] make "readline [] forever [basicprompt] end to basicprompt print [] print "READY print [] make "line basicread if emptyp :line [stop] ifelse numberp first :line [compile split :line] [immediate :line] end to compile :commands make "number first :commands make :number :line ifelse emptyp butfirst :commands ~ [eraseline :number] ~ [makedef (word "basic% :number) butfirst :commands] end to makedef :name :commands make "definition [[]] foreach :commands [run list (word "compile. first ?) ?] queue "definition (list "nextline :number) define :name :definition make "linenumbers insert :number :linenumbers end to insert :num :list if emptyp :list [output (list :num)] if :num = first :list [output :list] if :num < first :list [output fput :num :list] output fput first :list (insert :num butfirst :list) end to eraseline :num make "linenumbers remove :num :linenumbers end to immediate :line if equalp :line [list] [foreach :linenumbers [print thing ?] stop] if equalp :line [run] [run (list (word "basic% first :linenumbers)) stop] if equalp :line [exit] [throw "toplevel] print sentence [Invalid command:] :line end ;; Compiling each BASIC command to compile.end :command queue "definition [stop] end to compile.goto :command queue "definition (list (word "basic% last :command) "stop) end to compile.gosub :command queue "definition (list (word "basic% last :command)) end to compile.return :command queue "definition [stop] end to compile.print :command make "command butfirst :command while [not emptyp :command] [c.print1] queue "definition [print []] end to c.print1 make "exp expression ifelse equalp first first :exp "" ~ [make "sym gensym make word "%% :sym butfirst butlast first :exp queue "definition list "type word ":%% :sym] ~ [queue "definition fput "type :exp] if emptyp :command [stop] make "delimiter pop "command if equalp :delimiter ", [queue "definition [type char 9] stop] if equalp :delimiter "\; [stop] (throw "error [Comma or semicolon needed in print.]) end to compile.input :command make "command butfirst :command if equalp first first :command "" ~ [make "sym gensym make "prompt pop "command make word "%% :sym butfirst butlast :prompt queue "definition list "type word ":%% :sym] while [not emptyp :command] [c.input1] end to c.input1 make "var pop "command queue "definition (list "make (word ""% :var) "readvalue) if emptyp :command [stop] make "delimiter pop "command if not equalp :delimiter ", (throw "error [Comma needed in input.]) end to compile.let :command make "command butfirst :command make "var pop "command make "delimiter pop "command if not equalp :delimiter "= [(throw "error [Need = in let.])] make "exp expression queue "definition (sentence "make (word ""% :var) :exp) end to compile.for :command make "command butfirst :command make "var pop "command make "delimiter pop "command if not equalp :delimiter "= [(throw "error [Need = after for.])] make "start expression make "delimiter pop "command if not equalp :delimiter "to [(throw "error [Need to after for.])] make "end expression queue "definition (sentence "make (word ""% :var) :start) queue "definition (sentence "make (word ""let% :var) :end) make "newname word "% gensym queue "definition (sentence "make (word ""next% :var) (list (list :newname))) queue "definition (list :newname) define :name :definition make "name :newname make "definition [[]] end to compile.next :command make "command butfirst :command make "var pop "command queue "definition (sentence "make (word ""% :var) (word ":% :var) [+ 1]) queue "definition (sentence [if not greaterp] (word ":% :var) (word ":let% :var) (list (list "run (word ":next% :var) "stop))) end to compile.if :command make "command butfirst :command make "exp expression make "delimiter pop "command if not equalp :delimiter "then [(throw "error [Need then after if.])] queue "definition (sentence "if :exp (list c.if1)) end to c.if1 local "definition make "definition [[]] run list (word "compile. first :command) :command ifelse (count :definition) = 2 ~ [output last :definition] ~ [make "newname word "% gensym define :newname :definition output (list :newname)] end ;; Compile an expression for LET, IF, PRINT, or FOR to expression make "expr [] make "token expr1 while [not emptyp :token] [queue "expr :token make "token expr1] output :expr end to expr1 if emptyp :command [output []] make "token pop "command if memberp :token [+ - * / = < > ( )] [output :token] if memberp :token [, \; : then to] [push "command :token output []] if numberp :token [output :token] if equalp first :token "" [output :token] output word ":% :token end ;; reading input to basicread output basicread1 readword [] " end to basicread1 :input :output :token if emptyp :input [if not emptyp :token [push "output :token] output reverse :output] if equalp first :input "| | [if not emptyp :token [push "output :token] output basicread1 (butfirst :input) :output "] if equalp first :input "" [if not emptyp :token [push "output :token] output breadstring butfirst :input :output "] if memberp first :input [+ - * / = < > ( ) , \; :] ~ [if not emptyp :token [push "output :token] output basicread1 (butfirst :input) (fput first :input :output) "] output basicread1 (butfirst :input) :output (word :token first :input) end to breadstring :input :output :string if emptyp :input [(throw "error [String needs ending quote.])] if equalp first :input "" ~ [output basicread1 (butfirst :input) (fput (word "" :string "") :output) "] output breadstring (butfirst :input) :output (word :string first :input) end to split :line output fput first :line split1 (butfirst :line) [] [] end to split1 :input :output :command if emptyp :input [if not emptyp :command [push "output reverse :command] output reverse :output] if equalp first :input ": [if not emptyp :command [push "output reverse :command] output split1 (butfirst :input) :output []] output split1 (butfirst :input) :output (fput first :input :command) end ;; Runtime library to nextline :num make "target member :num :linenumbers if not emptyp :target [make "target butfirst :target] if not emptyp :target [run (list (word "basic% first :target))] end to readvalue while [emptyp :readline] [make "readline basicread] output pop "readline end