read.a68

CO data type and some operations for snailfish numbers CO
MODE PAIR = STRUCT (NUMBER left, right);
MODE NUMBER = UNION(INT, REF PAIR);

PROC make pair = (NUMBER x, y)REF PAIR:
  HEAP PAIR := (x,y);

PROC dump = (NUMBER data)VOID:
  CASE data IN
    (INT n):      printf(($g(0)$, n)),
    (REF PAIR p): (print("["); dump(left OF p); print(","); dump(right OF p); print("]"))
  ESAC;

PROC parse = (REF STRING s)NUMBER:
BEGIN
  CHAR c = s[1]; s := s[2:];
  IF c = "[" THEN
    NUMBER lt = parse (s); s := s[2:];
    NUMBER rt = parse (s); s := s[2:];
    make pair (lt, rt)
  ELSE
    INT p; char in string(c, p, "1234567890");
    p MOD 10
  FI
END;

[]NUMBER homework = BEGIN
  FLEX[0]NUMBER lines;
  on logical file end(stand in, (REF FILE f)BOOL: done reading);
  DO
    STRING s; read((s)); read(new line);
    ([UPB lines+1]NUMBER tmp; tmp[1:UPB lines] := lines; lines := tmp);
    lines[UPB lines] := parse(s)
  OD;
done reading:
  lines
END;