ex2

Exercise #2: Identifiers

Read the common instructions first if you have not read them. Don't forget to read the REPL section.

Download

sbt new kaist-plrg-cs320/identifiers.g8

Descriptions

Expressions are defined in core/src/main/scala/cs320/Expr.scala:

e ::= n
    | e + e
    | e - e
    | val x = e; e
    | x

• freeIds takes an expression and returns the set of every free identifier in the expression.

test(freeIds(Expr("{ val x = 1; (x + y) }")), Set("y"))
test(freeIds(Expr("{ val z = 2; 1 }")), Set())

• bindingIds takes an expression and returns the set of every binding identifier in the expression (whether or not the binding identifier is ever referenced by a bound identifier).

test(bindingIds(Expr("{ val x = 1; (x + y) }")), Set("x"))
test(bindingIds(Expr("{ val z = 2; 1 }")), Set("z"))

• boundIds takes an expression and returns the set of every bound identifier in the expression.

test(boundIds(Expr("{ val x = 1; (x + y) }")), Set("x"))
test(boundIds(Expr("{ val z = 2; 1 }")), Set())

Sample Solution

Implementation.scala