demos/calc-two, demos/calc-param: restore a one-line difference in lexer.mll.

I introduced this problem in a previous commit where I wanted to share the
lexer between several demos.

demos/calc-param/lexer.mll

-../calc/lexer.mll
\ No newline at end of file

demos/calc-param/lexer.mll

+{
+  open Tokens
+
+  exception Error of string
+
+}
+
+(* This rule looks for a single line, terminated with '\n' or eof.
+   It returns a pair of an optional string (the line that was found)
+   and a Boolean flag (false if eof was reached). *)
+
+rule line = parse
+| ([^'\n']* '\n') as line
+    (* Normal case: one line, no eof. *)
+    { Some line, true }
+| eof
+    (* Normal case: no data, eof. *)
+    { None, false }
+| ([^'\n']+ as line) eof
+    (* Special case: some data but missing '\n', then eof.
+       Consider this as the last line, and add the missing '\n'. *)
+    { Some (line ^ "\n"), false }
+
+(* This rule analyzes a single line and turns it into a stream of
+   tokens. *)
+
+and token = parse
+| [' ' '\t']
+    { token lexbuf }
+| '\n'
+    { EOL }
+| ['0'-'9']+ as i
+    { INT (int_of_string i) }
+| '+'
+    { PLUS }
+| '-'
+    { MINUS }
+| '*'
+    { TIMES }
+| '/'
+    { DIV }
+| '('
+    { LPAREN }
+| ')'
+    { RPAREN }
+| _
+    { raise (Error (Printf.sprintf "At offset %d: unexpected character.\n" (Lexing.lexeme_start lexbuf))) }
+| eof
+    { raise (Error (Printf.sprintf "At offset %d: unexpected end of input.\n" (Lexing.lexeme_start lexbuf))) }

demos/calc-two/lexer.mll

-../calc/lexer.mll
\ No newline at end of file
+../calc-param/lexer.mll
\ No newline at end of file