concatenation of words should preserve the data type represention when possible

[seblabbe]

This concerns word represented by str, tuple and list.

1. We want the representation of a concatenation of two words u and v to be preserved when u and v are of the same data type.

ACTUAL BEHAVIOR:

sage: u = Word(range(10))
sage: type(u)
<class 'sage.combinat.words.word.FiniteWord_list'>
sage: type(u*u)
<class 'sage.combinat.words.word.FiniteWord_callable_with_caching'>

sage: v = Word('asdgadsf')
sage: type(v)
<class 'sage.combinat.words.word.FiniteWord_str'>
sage: type(v*v)
<class 'sage.combinat.words.word.FiniteWord_callable_with_caching'>

sage: v = Word((2,3,5,21,34,6))
sage: type(v)
<class 'sage.combinat.words.word.FiniteWord_tuple'>
sage: type(v*v)
<class 'sage.combinat.words.word.FiniteWord_callable_with_caching'>

2. Moreover, the empty word could be ignored for concatenation :

ACTUAL BEHAVIOR:

sage: type(Word([]) * Word('asdga'))
<class 'sage.combinat.words.word.FiniteWord_callable_with_caching'>

INTENDED BEHAVIOR:

sage: type(Word([]) * Word('asdga'))
<class 'sage.combinat.words.word.FiniteWord_str'>

CC: @sagetrac-abmasse

Component: combinatorics

Keywords: word, concatenation

Author: Sébastien Labbé

Reviewer: Alexandre Blondin Massé

Merged: sage-4.3.4.alpha1

Issue created by migration from https://trac.sagemath.org/ticket/8233

[seblabbe]

Description changed:

--- 
+++ 
@@ -1,4 +1,8 @@
-This concerns word represented by str, tuple and list :
+This concerns word represented by str, tuple and list. 
+
+1. We want the representation of a concatenation of two words u and v to be preserved when u and v are of the same data type.
+
+ACTUAL BEHAVIOR:
 
 ```
 sage: u = Word(range(10))
@@ -23,3 +27,19 @@
 sage: type(v*v)
 <class 'sage.combinat.words.word.FiniteWord_callable_with_caching'>
 ```
+
+2. Moreover, the empty word could be ignored for concatenation :
+
+ACTUAL BEHAVIOR:
+
+```
+sage: type(Word([]) * Word('asdga'))
+<class 'sage.combinat.words.word.FiniteWord_callable_with_caching'>
+```
+
+INTENDED BEHAVIOR:
+
+```
+sage: type(Word([]) * Word('asdga'))
+<class 'sage.combinat.words.word.FiniteWord_str'>
+```

[seblabbe]

Forget about this patch!

[seblabbe]

Attachment: trac_8233_word_concatenation-sl.2.patch.gz

Depends on #7619.

[seblabbe]

comment:2

Attachment: trac_8233_word_concatenation-sl.patch.gz

[sagetrac-abmasse]

Reviewer: Alexandre Blondin Massé

[sagetrac-abmasse]

Changed keywords from none to word, concatenation

[sagetrac-abmasse]

comment:3

Tested on sage-4.3.3 after having applied ticket #7619. All tests passed, looking at the documentation with browse_sage_doc reveals nothing to be corrected. The improvement seems very reasonable and the code looks fine. Positive review !

[sagetrac-abmasse]

Author: Sébastien Labbé