Description

The goal of Homework #7 is to implement the interpreter of KXCFAE, which is the extended version of KCFAE with multiple arguments and eXceptions.

1           Multiple Arguments

Implement the interpreter to support multiple or zero arguments to a function, and multiple or zero arguments in a function call:

<KXCFAE> ::= …

| {fun {<id>*} <KXCFAE>}

| {<KXCFAE> <KXCFAE>*}

As usual, your interpreter should detect the mismatch between the numbers of function parameter and arguments at function calls and report an error that includes the words “wrong arity”. Note that, the function run takes an string, parses it, interprets it with an empty substitution, and produces a number string, a string “function” for closures or a string “continuation” for continuations.

Assume that each argument <id> is distinct for a fun expression. All continuations still accept a single argument. Example:

test(run(“{{fun {x y} {- y x}} 10 12}”), “2”) test(run(“{fun {} 12}”), “function”) testExc(run(“{{fun {x y} 1} 2}”), “wrong arity”) test(run(“{withcc esc {{fun {x y} x} 1 {esc 3}}}”), “3”)

2           Exceptions

Extend your language to support catching and throwing exceptions:

<KXCFAE> ::= …

| {try <KXCFAE> catch <KXCFAE>}

| {throw}

The try-catch form evaluates its first <KXCFAE> and returns its value âĂŤ unless evaluating the first <KXCFAE> throws an exception by evaluating throw, in which case the result of the try expression is the result of the second <KXCFAE>. Throw an error with the words “no enclosing try-catch” when throw is used without a dynamically enclosing try-catch from.

test(run(“{try 1 catch 2}”), “1”) test(run(“{try {throw} catch 2}”), “2”) test(run(“{try {+ 1 {throw}} catch 2}”), “2”)

test(run(“{{fun {f} {try {f} catch 1}} {fun {} {throw}}}”), 1) testExc(run(“{throw}”), “no enclosing try-catch”)

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