The Recursive Descent Parser

[eoredson]

Find attached What64 the recursive descent parser.

Erik.

[bplus]

Hi Erik,

Did you use this in your Interpreter SICK64D1.zip that I just downloaded?

[STxAxTIC]

Hey eoredson,

I've always liked this project. I'm glad you still occasionally make noise about it! Just curious - is there any formal website or home for this? Does the project *.zip contain all documentation?

And a really off-the-wall question is, just how much of the code is from the underscore-ridden QB64 era, vs how much is mostly QB45 compatible?

(I could dig a bit and answer all this myself, but I figure the public questions make things easier.)

Thanks!

[eoredson]

Thanks!

@bplus: Yes, it is the SICK engine.

STxAxTIC:
There is no web site I own that distributes it, and the .zip contains the entire project, including .doc

Interestingly enough, it was ported from 16-bit QB45 and that was not easy.

Unless https://goo.gl/pkQug8 qualifies as a web site..

Erik.

[Aurel]

SICK engine is large and filled with lot of stuff but i have have something smaller
well not written in qb64 but is quite universal ..
i hope that Mark(B+) can convert this to qb64...

Code: QB64: [Select]

1. 'recursive descent token evaluator
2. '#lookahead
3. int tc=0 : string token
4. string tokens[7]
5. tokens[1] = "2"
6. tokens[2] = "*"
7. tokens[3] = "("
8. tokens[4] = "3"
9. tokens[5] = "+"
10. tokens[6] = "4"
11. tokens[7] = ")"
12.  
13. sub gettok()
14. tc++ : token = tokens[tc]
15. end sub
16.  
17. sub expr() as float
18. float v = term()
19. if token = "+": gettok() : v = v + term(): end if
20. if token = "-": gettok() : v = v - term(): end if
21. return v
22. end sub
23.  
24. sub term() as float
25. float v = factor()
26. if token = "*": gettok() : v = v * factor(): end if
27. if token = "/": gettok() : v = v / factor(): end if
28. return v
29. end sub
30.  
31. sub factor() as float
32. float v
33. if asc(token)>47  and asc(token)<58 'nums
34. v = val(token) : gettok()
35. end if
36. if asc(token)=40 and asc(token)<>41 'match (...)
37. gettok() : v = expr() : gettok()
38. end if
39. return v
40. end sub
41.  
42. 'execute---------------
43. gettok() 'start
44. float res = expr()
45. print str res

[odin]

Posting code that's unusable in QB64 is not welcome. If the idea is awesome, adapt it to QB64 and post it or else just post it under off-topic.

[Aurel]

sorry i know that...
but i simply don't know how to translate this code to qb64.
I use Davs IDE .
main problem i have is with SUB routines
in another words i cannot figured proper shape..
i am looking into help of qb64 but i simply cannot found where is what?

[Aurel]

Here is what i transform but some things are wrong

Code: QB64: [Select]

1. recursive descent token evaluator
2. '
3. dim tc as INTEGER : dim token as string : dim v as single
4. DIM tokens() as string * 7
5. tokens(1) = "2"
6. tokens(2) = "*"
7. tokens(3) = "("
8. tokens(4) = "3"
9. tokens(5) = "+"
10. tokens(6) = "4"
11. tokens(7) = ")"
12.  
13. sub gettok()
14. tc=tc+1 : token = tokens(tc)
15. end sub
16.  
17. sub expr()
18. v = term()
19. if token = "+": gettok() : v = v + term(): end if
20. if token = "-": gettok() : v = v - term(): end if
21. return v
22. end sub
23.  
24. sub term()
25. v = factor()
26. if token = "*": gettok() : v = v * factor(): end if
27. if token = "/": gettok() : v = v / factor(): end if
28. return v
29. end sub
30.  
31. sub factor()
32. if asc(token)>47  and asc(token)<58 'nums
33. v = val(token) : gettok()
34. end if
35. if asc(token)=40 and asc(token)<>41 'match (...)
36. gettok() : v = expr() : gettok()
37. end if
38. return v
39. end sub
40.  
41. 'execute---------------
42. gettok() 'start
43. float res = expr()
44. print str(res)

[_vince]

What language is it? It looks interesting

[Aurel]

hi vince
it is o2( Oxygen basic)
all basic dialects are very similar and that is good
but i simply stuck with such a simple code here in qb64 ..my fault
or i become rusty .. :)

[jack]

Hi Aurel
here's your code translated to QB64

Code: QB64: [Select]

1. 'recursive descent token evaluator
2. DIM SHARED tc AS LONG
3. DIM SHARED tokens(8) AS STRING * 1
4. DIM SHARED token AS STRING
5.  
6. tc = 0
7. tokens(1) = "2"
8. tokens(2) = "*"
9. tokens(3) = "("
10. tokens(4) = "3"
11. tokens(5) = "+"
12. tokens(6) = "4"
13. tokens(7) = ")"
14.  
15. 'execute---------------
16. CALL gettok 'start
17. DIM res AS DOUBLE
18. res = expr#
19. PRINT res
20. END
21.  
22. SUB gettok ()
23.     tc = tc + 1
24.     token = tokens(tc)
25. END SUB
26.  
27. FUNCTION expr# ()
28.     DIM v AS DOUBLE
29.     v = term#
30.     IF token = "+" THEN
31.         gettok
32.         v = v + term#
33.     END IF
34.     IF token = "-" THEN
35.         gettok
36.         v = v - term#
37.     END IF
38.     expr# = v
39. END FUNCTION
40.  
41. FUNCTION term# ()
42.     DIM v AS DOUBLE
43.     v = factor#
44.     IF token = "*" THEN
45.         gettok
46.         v = v * factor#
47.     END IF
48.     IF token = "/" THEN
49.         gettok
50.         v = v / factor#
51.     END IF
52.     term# = v
53. END FUNCTION
54.  
55. FUNCTION factor# ()
56.     DIM v AS DOUBLE
57.     IF ASC(token) > 47 AND ASC(token) < 58 THEN 'nums
58.         v = VAL(token)
59.         gettok
60.     END IF
61.     IF ASC(token) = 40 AND ASC(token) <> 41 THEN 'match (...)
62.         gettok
63.         v = expr#
64.         gettok
65.     END IF
66.     factor# = v
67. END FUNCTION
68.  

output 14

[Aurel]

hi Jack and thank you!
now i see where is difference.
qb require # suffix for floating point number
globals need directive SHERED...
nice !

As we can see this few functions are really simple.

[bplus]

hi Jack and thank you!
now i see where is difference.
qb require # suffix for floating point number
globals need directive SHERED...
nice !

As we can see this few functions are really simple.

Aurel something else about QB64 subs and functions you should know:
The arguments passed are by default By Reference, NOT By Value so if you change a value in sub it might go back to main program changed.

[Aurel]

Hey Mark
I see now that something is different ..
ok so default is byRef...mean pointered.

[jack]

@Aurel
in your function factor the second if clause makes no sense, you can replace it with else, '(' and ')' are simply ignored by the function expr

Code: QB64: [Select]

1. FUNCTION factor# ()
2.     DIM v AS DOUBLE
3.     IF ASC(token) > 47 AND ASC(token) < 58 THEN 'nums
4.         v = VAL(token)
5.         gettok
6.     ELSE
7.         gettok
8.         v = expr#
9.         gettok
10.     END IF
11.     factor# = v
12. END FUNCTION
13.