[belyy_lis]

Hello everyone, I was given a lab to do in Visual Prolog. I have to make a calculator. Read from a text file and write to the list.
Is there a way to convert a string to a number?

[Thomas Linder Puls]

Given that the format match that of a Visual Prolog number you can use:

Code: Select all

Number = tryConvert(integer, String)

where integer could instead be for example real.

[belyy_lis]

Code: Select all

implement main
    open core, file, console, string
 
domains
    result_list = integer*.
 
class predicates
    culc : (inputStream) nondeterm.
    suM : (integer, integer).
    suB : (integer, integer).
    muL : (integer, integer).
    diV : (integer, integer).
 
clauses
    suM(F, S) :-
        X = F + S,
        write(X).
    suB(F, S) :-
        X = F - S,
        write(X).
    muL(F, S) :-
        X = F * S,
        write(X).
    diV(F, S) :-
        X = F / S,
        write(X).
 
    culc(In) :-
        In:endOfStream(),
        In:close(),
        !.
    culc(In) :-
        frontToken(In:readLine(), FirstParam, R),
        write(FirstParam),
        Number = tryConvert(integer, "2"),
        write(Number - 1),
        frontToken(R, Oper, SecondParam),
        write(Oper),
        write(SecondParam),
        culc(In).
 
clauses
    run() :-
        init(),
        In = inputStream_file::openFile8("sourceIn.txt"),
        culc(In),
        _ = readLine(),
        !
        or
        _ = readLine().
 
end implement main
 
goal
    console::run(main::run).

Type Action Description Filename Path
e504 The expression has type '::string', which is incompatible with the type '::integer' main.pro

[Thomas Linder Puls]

Sorry, I typed the wrong predicate, it should be:

Code: Select all

Number = tryToTerm(integer, String)

[belyy_lis]

Thank you so much. Now it counts, but only the first block works, in my case it is "+". How can I make it jump to the required block depending on the expression?

Code: Select all

implement main
    open core, console, string
 
domains
    result_list = integer*.
 
class predicates
    culc : (inputStream) nondeterm.
    suM : (integer, integer).
    suB : (integer, integer).
    muL : (integer, integer).
    diVi : (integer, integer).
 
clauses
    suM(F, S) :-
        X = F + S,
        write(X),
        nl.
    suB(F, S) :-
        X = F - S,
        write(X),
        nl.
    muL(F, S) :-
        X = F * S,
        write(X),
        nl.
    diVi(F, S) :-
        X = F / S,
        write(X),
        nl.
 
    culc(In) :-
        In:endOfStream(),
        In:close(),
        !.
 
    culc(In) :-
        frontToken(In:readLine(), FirstParam, R),
        frontToken(R, Oper, SecondParam),
        Oper = "+",
        F = tryToTerm(integer, FirstParam),
        S = tryToTerm(integer, SecondParam),
        suM(F, S),
        culc(In),
        !.
 
    culc(In) :-
        frontToken(In:readLine(), FirstParam, R),
        frontToken(R, Oper, SecondParam),
        Oper = "-",
        F = tryToTerm(integer, FirstParam),
        S = tryToTerm(integer, SecondParam),
        suB(F, S),
        culc(In).
 
    culc(In) :-
        frontToken(In:readLine(), FirstParam, R),
        frontToken(R, Oper, SecondParam),
        Oper = "*",
        F = tryToTerm(integer, FirstParam),
        S = tryToTerm(integer, SecondParam),
        muL(F, S),
        culc(In).
 
    culc(In) :-
        frontToken(In:readLine(), FirstParam, R),
        frontToken(R, Oper, SecondParam),
        Oper = "/",
        F = tryToTerm(integer, FirstParam),
        S = tryToTerm(integer, SecondParam),
        diVi(F, S),
        culc(In).
 
clauses
    run() :-
        init(),
        In = inputStream_file::openFile8("sourceIn.txt"),
        culc(In),
        _ = readChar(),
        !
        or
        _ = readLine().
 
end implement main
 
goal
    console::run(main::run).

[Harrison Pratt]

This would be a good time to learn how to use the debugger and walk through the code as it executes.

Put your cursor on the line with culc(In) in your run clause and press F9 to set a breakpoint.

Then press F5 (or click the single green triangle on the toolbar) to run the code in the debugger.

Press F10 to step through the code and see the execution flow. If you press Ctrl-Alt-V you can see the values of variables as they are created.

[Martin Meyer]

Yes, walk through the code by the debugger. Study the VIP Language Reference and tutorials. Doing so you will quickly become used to write programs in VIP.

One way to jump to required blocks depending on the expression would be (including some beautification):

Code: Select all

implement main
 
class predicates
    tryCalc : (string Line) -> integer Result determ.
clauses
    tryCalc(Line) = Result :-
        string::frontToken(Line, FirstParamStr, Line1),
        FirstParam = tryToTerm(FirstParamStr),
        string::frontToken(Line1, Oper, Line2),
        string::frontToken(Line2, SecondParamStr, Line3),
        SecondParam = tryToTerm(SecondParamStr),
        Line3 = "",
        try
            Result = tryCalc_evaluate(FirstParam, Oper, SecondParam)
        catch _TraceId do
            fail
        end try.
 
class predicates
    tryCalc_evaluate : (integer FirstParam, string Oper, integer SecondParam) -> integer Result determ.
clauses
    tryCalc_evaluate(FirstParam, "+", SecondParam) = FirstParam + SecondParam.
 
    tryCalc_evaluate(FirstParam, "-", SecondParam) = FirstParam - SecondParam.
 
    tryCalc_evaluate(FirstParam, "*", SecondParam) = FirstParam * SecondParam.
 
    tryCalc_evaluate(FirstParam, "/", SecondParam) = FirstParam div SecondParam.
 
clauses
    run() :-
        %init(), % a call to init is not necessary here in current VIP 9.0.6
        InStream = inputStream_file::openFileUtf8(@"..\sourceIn.txt"),
        Line = InStream:readLine(),
        InStream:close(),
        if Result = tryCalc(Line) then
            stdIo::write(Line, " = ", Result)
        else
            stdIo::write("Error in \"", Line, "\"")
        end if.
 
end implement main
 
goal
    console::runUtf8(main::run).

It assumes that you place the sourceIn.txt file in the project directory. Text files can be created and added to the project within the IDE.

[Gukalov]

Good evening.
Martin, integer can be negative.

Code: Select all

clauses
    run() :-
        if string::frontToken("-10+5", Token, Rest) then
            console::writef("Token = '%s'; Rest = '%s'", Token, Rest)
        end if,
        console::write("\n....................."),
        _ = console::readLine().
 
%  Token = '-'; Rest = '10+5'

[Martin Meyer]

Correct, integers can be negative. The language accepted in the example is but extremely simple. It accepts only number literals without leading signs.

Optional leading signs would make the example more complicated. Signed numbers are usually implemented in parsers through unary functions "-" and "+". Functions can be nested. For example -+--3 is a legal integer constant in VIP.

A full-blown parser for arithmetical expressions can be constructed with the LALR Parser Generator (in the Commercial Edition). However that is a lot more complicated than the tiny example.