Ruby代写: Project 401-Programming Languages

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Ruby Project 401-Programming Languages

Ruby Installation

Windows: Go to http://rubyinstaller.org/, and follow the instructions. For a quick and easy in- stall, click the <Download> button at the top of the page, and choose desired version under <RubyIn- stallers>

OS X: preinstalled Linux/Unix

􏰕 Install from package manager
􏰕 Go to www.ruby-lang.org/en/downloads/, and follow the instructions.

CIS: installed on vulcans

2 Assignment
Consider the following BNF for the Sim Programming Language (SimPL).

<program> <stmts>

<stmt>

<addop>

<mulop>

<factor>

<lexpr> <lterm> <lfactor>

<relop>

::= <stmts> ::= <stmt> ‘;’

| <stmt> ‘;’ <stmts> ::= identi􏰓er ‘:=’ <addop>

| ‘if’ <lexpr> ‘then’ <stmts> ‘end’
| ‘if’ <lexpr> ‘then’ <stmts> ‘else’ <stmts> ‘end’
| ‘for’ identi􏰓er ‘from’ <addop> ‘to’ <addop> ‘do’ <stmts> ‘end’
| ‘for’ identi􏰓er ‘from’ <addop> ‘to’ <addop> ‘by’ <addop> ‘do’ <stmts> ‘end’

::= <mulop> ‘+’ <addop> | <mulop> ‘-‘ <addop> | <mulop>

::= <factor> ‘*’ <mulop> | <factor> ‘/’ <mulop> | <factor>

::= integer
| identi􏰓er
| ‘(‘ <addop> ‘)’

::= <lterm> ‘and’ <lexpr> | <lterm>

::= ‘not’ <lfactor> | <lfactor>

::= ‘true’ | ‘false’

| <relop>
::= <addop> ‘<=’ <addop>

| <addop> ‘<‘ <addop> | <addop> ‘=’ <addop>

  • Write a lexer for the program language de􏰓nition. The lexer should have a getTokenKind() function that, when called, returns the symbol for the next sequential token (this function will be utilized in the next section). A symbol is a numeric value indicating the kind of token that was parsed. (e.g., one value for each keyword, operator, one value for all identi􏰓ers, one value for all integers, and one value for EOF.) In addition, the lexer should have a function getTokenText that returns the textual representation of the token. nextToken consumes the current token. The Lexer also needs to tack an `EOF’ (end of 􏰓le) token to the end of the list of tokens (this will also be used later).
    • 􏰕  separating by whitespace alone will not su􏰔ce as there may be instances such as 􏰑x:=5􏰒, which consists of three tokens, but will only be counted as one.
    • 􏰕  A SimPL identi􏰓er consists of letters (only alphabetic characters), digits, and underscores (_) with the restrictions that it must begin with a letter. SimPL comments are indicated by being preceded by (//) and terminated by the end of the line.
  • Create a recursive-descent syntax analyzer for the above language. Use the getTokenKind() and getTokenText() methods from the previous section to retrieve the tokens at each step. If the `EOF’ token is reach with no issue, the program should report that the 􏰓le is syntactically correct. Otherwise, if an error is found, an appropriate error message should be displayed.

    Assignment report: Turn in the source code of your project together with an assignment report. The assignment report should contain: (1) names of two team members including a short statement of work, (2) a description of your design, (3) what was di􏰔cult, (4) what did you like about Ruby, (5) what did you dislike about Ruby.

2

The following code should be a syntacticly correct SimPL program.

prev := 0; curr := 1;

for iter from 0 to N−1 do // iterative fibonacci tmp := prev + curr;
prev := curr ;

curr := tmp; end

;
The following is not a valid SimPL program. It contains a syntax error in every line.

prev := 0 curr := −1;

/ not a comment
for iter from 1 by 2 do

tmp := prev (+ curr); prev = curr ;
curr := ;

end

3

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