Spring 2001, CSE 428: Quiz 2.2 - 25 Jan 2001

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  1. [Points 1] What is the typical function of a scanner (circle only one answer, please)

    1. takes a parse tree and executes it
    2. takes a list of tokens and produces a parse tree
    3. translates the source code of a program into assembly code
    4. takes a program and produces a list of tokens
    5. takes a grammar and produces all possible parse trees

  2. [Points 1] What is the operational semantics of a programming language (circle only one answer, please)

    1. the grammar defining the language
    2. an abstract interpreter for the language
    3. the operations that the language is able to perform
    4. the definition of the static semantics of a program
    5. the operations performed by the compiler

  3. [Points 4] Consider the mini language of expressions seen in class, defined by the grammar 
       Exp ::=  Num | Ide | Exp Op Exp | let Ide = Num in Exp end
   Op  ::=  + | * | - | /
    where Num and Ide are defined as usual. For each of the following expressions, say whether or not they are derivable from this grammar. (Note: you are not requested to say whether an expression is "correct", but only whether it can be derived from the grammar.)

    1. let x = 1 in let x = 2 in x end       Not derivable
    2. let x = 1 + 2 in x end       Not derivable (declaration x = 1 + 2 not allowed)
    3. x + let x = 1 in x end       Derivable
    4. let x = 1 in x + let y = 1 in x end end       Derivable

  4. [Points 4] Consider the same language as in previous question, and the interpreter seen in class for that language. For each of the following expressions, say what is the result of the evaluation.

    1. let x = 2 in let x = 1 in x end end       1
    2. let x = 2 in let x = 1 in x end + x end       3
    3. let x = 2 in x end + let x = 1 in x end       3
    4. let x = 2 in x + let y = 1 in x + y end end       5