Databases
StackOverflow2013
Postsdbo
POUpdate2,Haskell
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POUpdate2,Haskell
    primarykey
    data
    text
    <ol> <li>Atom: The Atom is the datatype used to describe Atomic Sentences or propositions. These are basically represented as a string.</li> <li>Literal: Literals correspond to either atoms or negations of atoms. In this implementation each literal is represented as a pair consisting of a boolean value, indicating the polarity of the Atom, and the actual Atom. Thus, the literal ‘P’ is represented as (True,"P") whereas its negation ‘-P’ as (False,"P"). 2</li> <li>Clause: A Clause is a disjunction of literals, for example PvQvRv-S. In this implementation this is represented as a list of Literals. So the last clause would be [(True,"P"), (True,"Q"), (True,"R"),(False,"S")].</li> <li>Formula: A Formula is a conjunction of clauses, for example (P vQ)^(RvP v-Q)^(-P v-R). This is the CNF form of a propositional formula. In this implementation this is represented as a list of Clauses, so it is a list of lists of Literals. Our above example formula would be [[(True,"P"), (True,"Q")], [(True,"R"), (True,"P"), (False,"Q")], [(False, "P"), (False,"P")]].</li> <li>Model: A (partial) Model is a (partial) assignment of truth values to the Atoms in a Formula. In this implementation this is a list of (Atom, Bool) pairs, ie. the Atoms with their assignments. So in the above example of type Formula if we assigned true to P and false to Q then our model would be [("P", True),("Q", False)]</li> </ol> <p>Ok so I wrote and update function</p> <pre><code> update :: Node -&gt; [Node] </code></pre> <p>It takes in a Node and returns a list of the Nodes that result from assigning True to an unassigned atom in one case and False in the other (ie. a case split). The list returned has two nodes as elements. One node contains the formula with an atom assigned True and the model updated with this assignment, and the other contains the formula with the atom assigned False and the model updated to show this. The lists of unassigned atoms of each node are also updated accordingly. This function makes use of an assign function to make the assignments. It also uses the chooseAtom function to select the literal to assign.</p> <pre><code> update :: Node -&gt; [Node] update (formula, (atoms, model)) = [(assign (chooseAtom atoms, True) formula, (remove (chooseAtom atoms) atoms, ((chooseAtom atoms,True)) `insert` model)) , (assign (chooseAtom atoms, False) formula, (remove (chooseAtom atoms) atoms, ((chooseAtom atoms, False) `insert` model)) )] </code></pre> <p>Now I have to do the same thing but this time I must implement a variable selection heuristic.this should replace the chooseAtom and I'm supposed to write a function update2 using it</p> <pre><code> type Atom = String type Literal = (Bool,Atom) type Clause = [Literal] type Formula = [Clause] type Model = [(Atom, Bool)] type Node = (Formula, ([Atom], Model)) update2 :: Node -&gt; [Node] update2 = undefined </code></pre> <p>So my question is how can I create a heurestic and to implement it into the update2 function ,that shoud behave identical to the update function ?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USTKFALS
    1. USTKFALS
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POUpdate2,Haskell
      1. This table or related slice is empty.
      1. VTDownMod
    2. VO
      singulars
      1. POUpdate2,Haskell
      1. This table or related slice is empty.
      1. VTDownMod
    3. VO
      singulars
      1. POUpdate2,Haskell
      1. This table or related slice is empty.
      1. VTModeratorReview
    1. COWhat is this about? What are your `Node`, `Atom`, `Literal` and other types meant to represent?
      singulars
      1. POUpdate2,Haskell
      1. USAntoine Latter
    2. COThis doesn't seem to be a Haskell question. You know how to write functions in Haskell. What you don't know is how to write a function that implements a variable selection heuristic. Neither do we: it is not part of Haskell, it is part of your problem domain.
      singulars
      1. POUpdate2,Haskell
      1. USdave4420
    3. COI wrote as concise as possible....should I add other details?My main concern is writting the heurestic,because this is all the info that I have....so if you find the problem ambiguous then now you know why I asked for help...
      singulars
      1. POUpdate2,Haskell
      1. USTKFALS
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload