Consider the following grammar: (//some alternative rules are listed on separate lines without using symbol |):

stmt > assignment

> subr call

assignment > id := expr

subr call > id ( arg list )

expr > primary expr tail

expr tail > op expr

>

primary > id

> subr call

> ( expr )

op > + | - | * | /

arg list > expr args tail

args tail > , arg list

>

(a) Construct a parse tree for the input string foo(a,b).

(b) Give a canonical (right-most) derivation of this same string.

(c) Prove that the grammar is not LL(1). (//hint: find an example that LL(1) does not work).

(d) Modify the grammar so that it is LL(1). (//hint: use left factoring)