Support datum_coment

First step

Rewrite Reader.y in a way that R7RS describes list and dot list.

〈datum〉 −→ 〈simple datum〉 | 〈compound datum〉
| 〈label〉 = 〈datum〉 | 〈label〉 #
〈simple datum〉 −→ 〈boolean〉 | 〈number〉
| 〈character〉 | 〈string〉 | 〈symbol〉 | 〈bytevector〉
〈symbol〉 −→ 〈identifier〉
〈compound datum〉 −→ 〈list〉 | 〈vector〉 | 〈abbreviation〉
〈list〉 −→ (〈datum〉*) | (〈datum〉+ . 〈datum〉)
〈abbreviation〉 −→ 〈abbrev prefix〉 〈datum〉
〈abbrev prefix〉 −→ ’ | ` | , | ,@
〈vector〉 −→ #(〈datum〉*)
〈label〉 −→ # 〈uinteger 10〉

How do you express * and + in Bison grammer?

Per https://stackoverflow.com/questions/29235967/bison-one-or-more-occurrences-in-grammar-file

One or more:

declarations
    : declaration
    | declarations declaration
    ;

Zero or more:

declarations
    : /* empty */
    | declarations declaration
    ;

How to debug

• parsing - How can I debug my flex/bison grammar? - Stack Overflow

Debugging (Bison 3.8.1)

• Algorithm (Bison 3.8.1)
  • shift: push tokens to stack
  • reduce: matched a group of tokens is replaced by one token(= lhs in the grammer) in the stack.
  • reduce continues until the entire input down to a single grouping which is start symbol.
  • Lookahead (Bison 3.8.1)
    • lookahead token is stored in yychar.
  • Shift/Reduce (Bison 3.8.1)
    • if shift/reduce conflicts, the parse chooses shift. eg) if expr then stmt else vs if expr then
  • Precedence (Bison 3.8.1)
    • Why Precedence (Bison 3.8.1)
    • Using Precedence (Bison 3.8.1)
      • Use %left or %right to let the parser know your choice.
    • Precedence Only (Bison 3.8.1)
    • Precedence Examples (Bison 3.8.1)
    • How Precedence (Bison 3.8.1)
    • Non Operators (Bison 3.8.1)
  • Contextual Precedence (Bison 3.8.1)
    • %prec
  • Parser States (Bison 3.8.1)
  • Reduce/Reduce (Bison 3.8.1)
    • reduce/reduce conflict. Bison chooses to use the rule that appears first in the grammer file.
    • REREAD THIS
  • Mysterious Conflicts (Bison 3.8.1)
    • REREAD THIS
  • Tuning LR (Bison 3.8.1)
  • Generalized LR Parsing (Bison 3.8.1)
  • Memory Management (Bison 3.8.1)
• Counterexamples (Bison 3.8.1)
• Graphviz (Bison 3.8.1)
• Xml (Bison 3.8.1)
• Debugging (Bison 3.8.1)
  • Tracing (Bison 3.8.1)
    • Enabling Traces (Bison 3.8.1)
    • Mfcalc Traces (Bison 3.8.1)
      • Might be useful later.