reader.lg

load "../logo/types.lg

make "open_paren_char    char 40
make "close_paren_char   char 41
make "open_bracket_char  char 91
make "close_bracket_char char 93
make "open_brace_char    char 123
make "close_brace_char   char 125

to newlinep :char
output case ascii :char [
  [[10 13] "true]
  [else "false]
]
end

to whitespacep :char
output case ascii :char [
  [[9 10 13 32] "true]
  [else "false]
]
end

to singlechartokenp :char
output case :char [
  [[ ( ) \[ \] \{ \} ' ` \^ @ ] "true]
  [else "false]
]
end

to separatorp :char
output ifelse whitespacep :char [
  "true
] [
  case :char [
    [[ ( ) \[ \] \{ \} ' \" ` , \; ] "true]
    [else "false]
  ]
]
end

to read_comment_token :s
localmake "rest :s
while [not emptyp :rest] [
  localmake "c first :rest
  ifelse newlinep :c [
    output list " butfirst :rest
  ] [
    make "rest butfirst :rest
  ]
]
output list " :rest
end

to read_word_token :s
localmake "w "
localmake "rest :s
while [not emptyp :rest] [
  localmake "c first :rest
  ifelse separatorp :c [
    output list :w :rest
  ] [
    make "w word :w :c
    make "rest butfirst :rest
  ]
]
output list :w :rest
end

to read_string_token :s
localmake "w first :s
localmake "rest butfirst :s
while [not emptyp :rest] [
  localmake "c first :rest
  if :c = "" [
    make "w word :w :c
    output list :w butfirst :rest
  ]
  if :c = "\\ [
    make "w word :w :c
    make "rest butfirst :rest
    make "c first :rest
  ]
  make "w word :w :c
  make "rest butfirst :rest
]
(throw "error [Expected closing quotes])
end

to read_next_token :s
localmake "c first :s
localmake "rest butfirst :s
output cond [
  [[whitespacep :c]      list " :rest]
  [[:c = ",]             list " :rest]
  [[:c = "~]             ifelse ((first :rest) = "@) [list "~@ butfirst :rest] [list "~ :rest] ]
  [[singlechartokenp :c] list :c :rest]
  [[:c = "\;]            read_comment_token :s]
  [[:c = ""]             read_string_token :s]
  [else                  read_word_token :s]
]
output list first :s butfirst :s
end

to tokenize :str
localmake "tokens []
localmake "s :str
while [not emptyp :s] [
  localmake "res read_next_token :s
  localmake "token first :res
  make "s last :res
  if not emptyp :token [
    make "tokens lput :token :tokens
  ]
]
output :tokens
end

to reader_new :tokens
output listtoarray list :tokens 1
end

to reader_peek :reader
localmake "tokens item 1 :reader
localmake "pos item 2 :reader
if :pos > count :tokens [output []]
output item :pos :tokens
end

to reader_next :reader
make "token reader_peek :reader
localmake "pos item 2 :reader
setitem 2 :reader (1 + :pos)
output :token
end

to unescape_string :token
localmake "s butfirst butlast :token ; remove surrounding double-quotes
localmake "i 1
localmake "res "
while [:i <= count :s] [
  localmake "c item :i :s
  ifelse :c = "\\ [
    make "i (:i + 1)
    make "c item :i :s
    make "res word :res case :c [
      [[ n ] char 10]
      [[ " ] "\" ]
      [[ \\ ] "\\ ]
      [else :c]
    ]
  ] [
    make "res word :res :c
  ]
  make "i (:i + 1)
]
output :res
end

to read_atom :reader
localmake "token reader_next :reader
output cond [
  [[:token = "nil]         nil_new]
  [[:token = "true]        true_new]
  [[:token = "false]       false_new]
  [[numberp :token]        obj_new "number :token]
  [[(first :token) = ": ]  obj_new "keyword butfirst :token]
  [[(first :token) = "\" ] obj_new "string unescape_string :token]
  [else                    symbol_new :token]
]
end

to read_seq :reader :value_type :start_char :end_char
localmake "token reader_next :reader
if :token <> :start_char [(throw "error sentence "expected (word "' :start_char "'))]
localmake "seq []
make "token reader_peek :reader
while [:token <> :end_char] [
  if emptyp :token [(throw "error (sentence [expected] (word "' :end_char "',) [got EOF]))]
  make "seq lput read_form :reader :seq
  make "token reader_peek :reader
]
ignore reader_next :reader
output obj_new :value_type :seq
end

to reader_macro :reader :symbol_name
ignore reader_next :reader
output obj_new "list list symbol_new :symbol_name read_form :reader
end

to with_meta_reader_macro :reader
ignore reader_next :reader
localmake "meta read_form :reader
output obj_new "list (list symbol_new "with-meta read_form :reader :meta)
end

to read_form :reader
output case reader_peek :reader [
  [[ ' ]   reader_macro :reader "quote ]
  [[ ` ]   reader_macro :reader "quasiquote ]
  [[ ~ ]   reader_macro :reader "unquote ]
  [[ ~@ ]  reader_macro :reader "splice-unquote ]
  [[ \^ ]   with_meta_reader_macro :reader ]
  [[ @ ]   reader_macro :reader "deref ]
  [[ ( ]   read_seq :reader "list :open_paren_char :close_paren_char ]
  [[ ) ]   (throw "error sentence [unexpected] (word "' :close_paren_char "')) ]
  [[ \[ ]  read_seq :reader "vector :open_bracket_char :close_bracket_char ]
  [[ \] ]  (throw "error sentence [unexpected] (word "' :close_bracket_char "')) ]
  [[ \{ ]  read_seq :reader "hashmap :open_brace_char :close_brace_char ]
  [[ \} ]  (throw "error sentence [unexpected] (word "' :close_brace_char "')) ]
  [else    read_atom :reader]
]
end

to read_str :str
localmake "tokens tokenize :str
if emptyp :tokens [output []]
localmake "reader reader_new :tokens
output read_form :reader
end