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PetitParser problem with plus

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jgfoster

PetitParser problem with plus

There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

Guillaume Larcheveque

Re: PetitParser problem with plus

With x, x it will only go to 2 level deep.

With the plus you allow to go as far as the x rule succeed and your x rule always succeed because notA always succeed due to the star without consuming anything so you fall into infinite loop.

2014-12-18 6:47 GMT+01:00 James Foster <[hidden email]>:

There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

Guillaume Larcheveque

Guillaume Larcheveque

Re: PetitParser problem with plus

So you just have to remove the #star in notA or replace it by #plus to makes it succeed only when it consume at least one character

2014-12-18 7:54 GMT+01:00 Guillaume Larcheveque <[hidden email]>:

With x, x it will only go to 2 level deep.

With the plus you allow to go as far as the x rule succeed and your x rule always succeed because notA always succeed due to the star without consuming anything so you fall into infinite loop.

2014-12-18 6:47 GMT+01:00 James Foster <[hidden email]>:
There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

--
Guillaume Larcheveque

Guillaume Larcheveque

kurs.jan

Re: PetitParser problem with plus

Exactly...

This happens so often that we should add some warning somewhere in these cases....

Cheers,

Jan

On 18 December 2014 at 08:36, Guillaume Larcheveque <[hidden email]> wrote:

So you just have to remove the #star in notA or replace it by #plus to makes it succeed only when it consume at least one character

2014-12-18 7:54 GMT+01:00 Guillaume Larcheveque <[hidden email]>:
With x, x it will only go to 2 level deep.

With the plus you allow to go as far as the x rule succeed and your x rule always succeed because notA always succeed due to the star without consuming anything so you fall into infinite loop.

2014-12-18 6:47 GMT+01:00 James Foster <[hidden email]>:
There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

--
Guillaume Larcheveque

--
Guillaume Larcheveque

jgfoster

Re: PetitParser problem with plus

In reply to this post by Guillaume Larcheveque

That did it and it makes sense. Thanks so much!

On Dec 17, 2014, at 11:36 PM, Guillaume Larcheveque <[hidden email]> wrote:

So you just have to remove the #star in notA or replace it by #plus to makes it succeed only when it consume at least one character

2014-12-18 7:54 GMT+01:00 Guillaume Larcheveque <[hidden email]>:
With x, x it will only go to 2 level deep.

With the plus you allow to go as far as the x rule succeed and your x rule always succeed because notA always succeed due to the star without consuming anything so you fall into infinite loop.

2014-12-18 6:47 GMT+01:00 James Foster <[hidden email]>:
There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

--
Guillaume Larcheveque

--
Guillaume Larcheveque

stepharo

Re: PetitParser problem with plus

In reply to this post by kurs.jan

Could one of you write a small paragraph for the petit parser chapter?

Le 18/12/14 09:07, Jan Kurš a écrit :

Exactly...

This happens so often that we should add some warning somewhere in these cases....

Cheers,

Jan

On 18 December 2014 at 08:36, Guillaume Larcheveque <[hidden email]> wrote:

So you just have to remove the #star in notA or replace it by #plus to makes it succeed only when it consume at least one character

2014-12-18 7:54 GMT+01:00 Guillaume Larcheveque <[hidden email]>:

With x, x it will only go to 2 level deep.

With the plus you allow to go as far as the x rule succeed and your x rule always succeed because notA always succeed due to the star without consuming anything so you fall into infinite loop.

2014-12-18 6:47 GMT+01:00 James Foster <[hidden email]>:
There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

--

Guillaume Larcheveque

--

Guillaume Larcheveque

kurs.jan

Re: PetitParser problem with plus

You mean deep into pharo? Or something else? I can do this...

On 21 December 2014 at 13:27, stepharo <[hidden email]> wrote:

Could one of you write a small paragraph for the petit parser chapter?

Le 18/12/14 09:07, Jan Kurš a écrit :

Exactly...

This happens so often that we should add some warning somewhere in these cases....

Cheers,

Jan

On 18 December 2014 at 08:36, Guillaume Larcheveque <[hidden email]> wrote:

So you just have to remove the #star in notA or replace it by #plus to makes it succeed only when it consume at least one character

2014-12-18 7:54 GMT+01:00 Guillaume Larcheveque <[hidden email]>:

With x, x it will only go to 2 level deep.

With the plus you allow to go as far as the x rule succeed and your x rule always succeed because notA always succeed due to the star without consuming anything so you fall into infinite loop.

2014-12-18 6:47 GMT+01:00 James Foster <[hidden email]>:
There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

--

Guillaume Larcheveque

--

Guillaume Larcheveque

stepharo

Re: PetitParser problem with plus

Le 31/12/14 16:37, Jan Kurš a écrit :

You mean deep into pharo? Or something else? I can do this...

Yes I mean let us improve **OUR** documentation.
Soon we will release an official version of Deep into Pharo. Then we will convert it to pillar and this means that we will
all the Pharo books online and on different formats.

Stef

On 21 December 2014 at 13:27, stepharo <[hidden email]> wrote:

Could one of you write a small paragraph for the petit parser chapter?

Le 18/12/14 09:07, Jan Kurš a écrit :

Exactly...

This happens so often that we should add some warning somewhere in these cases....

Cheers,

Jan

On 18 December 2014 at 08:36, Guillaume Larcheveque <[hidden email]> wrote:

So you just have to remove the #star in notA or replace it by #plus to makes it succeed only when it consume at least one character

2014-12-18 7:54 GMT+01:00 Guillaume Larcheveque <[hidden email]>:

With x, x it will only go to 2 level deep.

With the plus you allow to go as far as the x rule succeed and your x rule always succeed because notA always succeed due to the star without consuming anything so you fall into infinite loop.

2014-12-18 6:47 GMT+01:00 James Foster <[hidden email]>:
There is something about plus that I don’t understand. In the following code if I parse for (x , x) then I get what I expect. If I parse for (x plus) then the image hangs. What am I doing wrong?

James

| a notA x y |
a := $a asParser.
notA := $a asParser negate star flatten.
x := a / notA.
y := x , x. “works fine”
y := x plus. “never finishes”
^y end parse: 'ab’.

--

Guillaume Larcheveque

--

Guillaume Larcheveque