DCGJavaParser

Using Prolog, this is a parser for a definite clause grammar of Java-Light.

Java-Light is a fragment of Java consisting of non-empty semi-colon-separated sequences of some grammatical Java statements. In particular, we restrict ourselves to the following Java statements:

• Assignment statements example:

_n1 = 13;
_n2 = 21;

fib = _n1 + _n2;

_n1 = _n2;
_n2 = fib;

Prolog query:

s(T,[_,n,1, =, 13,;, _,n,2, =, 21,;, f,i,b, =, _,n,1, +, _,n,2,;, _,n,1, =, _,n,2,;, _,n,2, =, f,i,b,;],[]).

Output:

T = s([assign(id([65, n, 1]), =, int(13), ;), assign(id([65, n, 2]), =, int(21), ;), assign(id([f, i, b]), =, exprs(id([65, n, 1]), exprsRest(+, id([65, n, 2]))), ;), assign(id([65, n, 1]), =, id([65, n, 2]), ;), assign(id([65, n, 2]), =, id([f, i, b]), ;)])

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• Java if and if-else statements, nested to any depth, and with bodies which are single statements.

if (n == 0 )
  fib = 0;
if (n == 1 )
  fib = 1;

// another example - nested if (note that we don't handle dangling else problem)
if (n % 2 == 0)
  if( n != 0 )
    x = 1
else
  x = 0
    

Prolog query for the first example:

s(T,['if','(',n, ==, 0, ')',  f,i,b, =, 0,;, 'if','(',n, ==, 1,')', f,i,b, =, 1,;],[]).

Output:

T = s([ifStatement(if, '(', cdn(id([n]), ==, int(0)), ')', ifbody(assign(id([f, i, b]), =, int(0), ;))), ifStatement(if, '(', cdn(id([n]), ==, int(1)), ')', ifbody(assign(id([f, i|...]), =, int(1), ;)))]) .

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• Java while loops, nested to any depth, and with bodies which are single statements (assignment/while/if).

while(i <= num)
  i = i + _n2;

Prolog query:

s(T,[while, '(', i, <=, n,u,m,')',  i, =, i, +, _,n,2,;],[]).

Output:

T = s([whileLoop(while, '(', cdn(id([i]), <=, id([n, u, m])), ')', loopBody(assign(id([i]), =, exprs(id([i]), exprsRest(+, id([65, n, 2]))), ;)))])

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How to test:

correctStatements.txt contains prolog queries that should return a parse tree, while incorrectStatements.txt contains incorrect ones that should return false.

To test the queries, open the file eval.py and replace the parameter test_file_name with either correctStatements.txt or incorrectStatements.txt. Next, run the file to test all the queries.

NB: The evaluation code assumes that the queries in the file are correctly formatted and can be evaluated by Prolog.