‣ IsJuliaObject( obj ) | ( filter ) |
Returns: true or false
The result is true if and only if obj is a pointer to a Julia object.
The results of JuliaModule (2.3-3) are always in IsJuliaObject.
gap> julia_fun:= JuliaEvalString( "sqrt" ); <Julia: sqrt> gap> IsJuliaObject( julia_fun ); true gap> julia_val:= julia_fun( 2 ); <Julia: 1.4142135623730951> gap> IsJuliaObject( julia_val ); true gap> julia_x:= JuliaEvalString( "x = 4" ); 4 gap> IsJuliaObject( julia_x ); false gap> IsJuliaObject( JuliaModule( "Main" ) ); true
‣ IsJuliaWrapper( obj ) | ( filter ) |
Returns: true or false
If the component or positional object obj is in this filter then calling a Julia function with obj as an argument will not pass obj as an GapObj, but instead its JuliaPointer (2.1-3) value is passed, which must be a Julia object. This admits implementing high-level wrapper objects for Julia objects that behave just like the Julia objects when used as arguments in calls to Julia functions.
Objects in IsJuliaWrapper should not be in the filter IsJuliaObject (2.1-1).
Examples of objects in IsJuliaWrapper are the return values of JuliaModule (2.3-3).
‣ JuliaPointer( obj ) | ( attribute ) |
is an attribute for GAP objects in the filter IsJuliaWrapper (2.1-2). The value must be a Julia object.
gap> Julia; <Julia module Main> gap> IsJuliaObject( Julia ); false gap> IsJuliaWrapper( Julia ); true gap> ptr:= JuliaPointer( Julia ); <Julia: Main> gap> IsJuliaObject( ptr ); true
‣ IsJuliaModule( obj ) | ( filter ) |
Returns: true or false
This filter is set in those GAP objects that represent Julia modules. Members of a Julia module can be accessed like record components.
gap> IsJuliaModule( Julia ); true gap> Julia.GAP; <Julia module GAP> gap> IsJuliaModule( Julia.GAP ); true gap> Julia.GAP.julia_to_gap; <Julia: julia_to_gap> gap> JuliaFunction( "julia_to_gap", "GAP" ); # the same function <Julia: julia_to_gap>
‣ JuliaEvalString( string ) | ( function ) |
evaluates the string string in the current Julia session, in the Main module, and returns Julia's return value.
gap> JuliaEvalString( "x = 2^2" ); # assignment to a variable in Julia 4 gap> JuliaEvalString( "x" ); # access to this variable 4
‣ JuliaIncludeFile( filename[, module_name] ) | ( function ) |
Returns: nothing.
calls Julia's Base.include with the strings filename (an absolute filename, as returned by Filename (Reference: Filename)) and module_name (the name of a Julia module, the default is "Main"). This means that the Julia code in the file with name filename gets executed in the current Julia session, in the context of the Julia module module_name.
‣ JuliaImportPackage( pkgname ) | ( function ) |
Returns: true or false.
This function triggers the execution of an import statement for the Julia package with name pkgname. It returns true if the call was successful, and false otherwise.
Note that we just want to load the package into Julia, we do not want to import variable names from the package into Julia's Main module, because the Julia variables must be referenced relative to their modules if we want to be sure to access the correct values.
Why is this function needed?
Apparently libjulia throws an error when trying to compile the package, which happens when some files from the package have been modified since compilation.
Thus GAP has to check whether the Julia package has been loaded successfully, and can then safely load and execute code that relies on this Julia package. In particular, we cannot just put the necessary import statements into the relevant .jl files, and then load these files with JuliaIncludeFile (2.2-2).
‣ JuliaFunction( function_name[, module_name] ) | ( function ) |
Returns: a function
Returns a GAP function that wraps the Julia function with identifier function_name from the module module_name. Both arguments must be strings. If module_name is not given, the function is taken from Julia's Main module.
gap> fun:= JuliaFunction( "sqrt" ); <Julia: sqrt> gap> Print( fun ); function ( arg... ) <<kernel code>> from Julia:sqrt end gap> IsFunction( fun ); true gap> IsJuliaObject( fun ); false
Alternatively, one can access Julia functions also via the global object Julia (2.3-2), as follows.
gap> Julia.sqrt; <Julia: sqrt>
Note that each call to JuliaFunction and each component access to Julia (2.3-2) create a new GAP object.
gap> IsIdenticalObj( JuliaFunction( "sqrt" ), JuliaFunction( "sqrt" ) ); false gap> IsIdenticalObj( Julia.sqrt, Julia.sqrt ); false
‣ Julia | ( global variable ) |
This global variable represents the Julia module Main, see IsJuliaModule (2.1-4).
The variables from the underlying Julia session can be accessed via Julia, as follows.
gap> Julia.sqrt; # a Julia function <Julia: sqrt> gap> JuliaEvalString( "x = 1" ); # an assignment in the Julia session 1 gap> Julia.x; # access to the value that was just assigned 1 gap> Julia.Main.x; 1
‣ JuliaModule( name ) | ( function ) |
Returns: a Julia object
Returns the Julia object that points to the Julia module with name name.
gap> gapmodule:= JuliaModule( "GAP" ); <Julia: GAP> gap> gapmodule = JuliaPointer( Julia.GAP ); true
‣ JuliaTypeInfo( juliaobj ) | ( function ) |
Returns: a string.
Returns the string that describes the Julia type of the object juliaobj.
gap> JuliaTypeInfo( Julia.GAP ); "Module" gap> JuliaTypeInfo( JuliaPointer( Julia.GAP ) ); "Module" gap> JuliaTypeInfo( JuliaEvalString( "sqrt(2)" ) ); "Float64" gap> JuliaTypeInfo( 1 ); "Int64"
‣ CallJuliaFunctionWithCatch( juliafunc, arguments ) | ( function ) |
Returns: a record.
The function calls the Julia function juliafunc with arguments in the GAP list arguments, and returns a record with the components ok and value. If no error occurred then ok has the value true, and value is the value returned by juliafunc. If an error occurred then ok has the value false, and value is the error message as a GAP string.
gap> fun:= Julia.sqrt;; gap> CallJuliaFunctionWithCatch( fun, [ 2 ] ); rec( ok := true, value := <Julia: 1.4142135623730951> ) gap> res:= CallJuliaFunctionWithCatch( fun, [ -1 ] );; gap> res.ok; false gap> res.value{ [ 1 .. Position( res.value, '(' )-1 ] }; "DomainError" gap> inv:= Julia.inv;; gap> m:= GAPToJulia( JuliaEvalString( "Matrix{Int}" ), [[1,2],[2,4]] ); <Julia: [1 2; 2 4]> gap> res:= CallJuliaFunctionWithCatch( inv, [ m ] );; gap> res.ok; false gap> res.value{ [ 1 .. Position( res.value, '(' )-1 ] }; "LinearAlgebra.SingularException"
‣ CallJuliaFunctionWithKeywordArguments( juliafunc, arguments, arec ) | ( function ) |
Returns: the result of the Julia function call.
The function calls the Julia function juliafunc with ordinary arguments in the GAP list arguments and keyword arguments given by the component names (keys) and values of the record arec, and returns the function value.
Note that the entries of arguments and the components of arec are not implicitly converted to Julia.
gap> CallJuliaFunctionWithKeywordArguments( Julia.Base.round, > [ GAPToJulia( Float( 1/3 ) ) ], rec( digits:= 5 ) ); <Julia: 0.33333> gap> CallJuliaFunctionWithKeywordArguments( > Julia.Base.range, [ 2 ], rec( length:= 5, step:= 2 ) ); <Julia: 2:2:10> gap> m:= GAPToJulia( JuliaEvalString( "Matrix{Int}" ), > [ [ 1, 2 ], [ 3, 4 ] ] ); <Julia: [1 2; 3 4]> gap> CallJuliaFunctionWithKeywordArguments( > Julia.Base.reverse, [ m ], rec( dims:= 1 ) ); <Julia: [3 4; 1 2]> gap> CallJuliaFunctionWithKeywordArguments( > Julia.Base.reverse, [ m ], rec( dims:= 2 ) ); <Julia: [2 1; 4 3]> gap> tuptyp:= JuliaEvalString( "Tuple{Int,Int}" );; gap> t1:= GAPToJulia( tuptyp, [ 2, 1 ] ); <Julia: (2, 1)> gap> t2:= GAPToJulia( tuptyp, [ 1, 3 ] ); <Julia: (1, 3)> gap> CallJuliaFunctionWithKeywordArguments( > Julia.Base.( "repeat" ), [ m ], > rec( inner:= t1, outer:= t2 ) ); <Julia: [1 2 1 2 1 2; 1 2 1 2 1 2; 3 4 3 4 3 4; 3 4 3 4 3 4]>
The simplest way to execute Julia code from GAP is to call JuliaEvalString (2.2-1) with a string that contains the Julia code in question.
gap> JuliaEvalString( "sqrt( 2 )" ); <Julia: 1.4142135623730951>
However, it is usually more suitable to create GAP variables whose values are Julia objects, and to call Julia functions directly. The GAP function call syntax is used for that.
gap> jsqrt:= JuliaEvalString( "sqrt" ); <Julia: sqrt> gap> jsqrt( 2 ); <Julia: 1.4142135623730951>
In fact, there are slightly different kinds of function calls. A Julia function such as Julia.sqrt (or equivalently JuliaFunction( "sqrt" )) is represented by a GAP function object, and calls to it are executed on the C level, using Julia's jl_call.
gap> fun:= Julia.sqrt; <Julia: sqrt> gap> IsJuliaObject( fun ); false gap> IsFunction( fun ); true gap> fun( 2 ); <Julia: 1.4142135623730951>
Note that in Julia any object (not just functions) is potentially callable (in fact this is the same as in GAP), for example Julia types can be
gap> smalltype:= Julia.Int32; <Julia: Int32> gap> IsJuliaObject( smalltype ); true gap> IsFunction( smalltype ); false gap> val:= smalltype( 1 ); <Julia: 1> gap> JuliaTypeInfo( val ); "Int32" gap> JuliaTypeInfo( 1 ); "Int64"
For the following operations, methods are installed that require arguments in IsJuliaObject (2.1-1) and delegate to the corresponding Julia functions.
CallFuncList (Reference: CallFuncList), delegating to Julia.Core._apply (this yields the function call syntax in GAP, it is installed also for objects in IsJuliaWrapper (2.1-2),
access to and assignment of entries of arrays, via \[\] (Reference: \[\]), \[\]\:\= (Reference: \[\]\:\=), and the (up to GAP 4.11 undocumented) operations MatElm and SetMatElm, delegating to Julia.Base.getindex and Julia.Base.setindex,
access to and assignment of fields and properties, via \. (Reference: \.) and \.\:\= (Reference: \.\:\=), delegating to Julia.Base.getproperty and Julia.Base.setproperty,
the unary arithmetic operations AdditiveInverseOp (Reference: AdditiveInverseOp), ZeroOp (Reference: ZeroOp), and OneOp (Reference: OneOp), delegating to Julia.Base.\-, Julia.Base.zero, and Julia.Base.one,
the binary arithmetic operations \+ (Reference: +), \- (Reference: -), \* (Reference: *), \/ (Reference: /), LeftQuotient (Reference: LeftQuotient), \^ (Reference: ^), \= (Reference: \=), \< (Reference: \<), delegating to Julia.Base.\+, Julia.Base.\-, Julia.Base.\*, Julia.Base.\/, Julia.Base.\\, Julia.Base.\^, Julia.Base.\=\=, and Julia.Base.\<; the same methods are installed also for the case that only one argument is in IsJuliaObject (2.1-1), and the other argument is an immediate integer.
gap> m:= GAPToJulia( JuliaEvalString( "Matrix{Int}" ), > [ [ 1, 2 ], [ 3, 4 ] ] ); <Julia: [1 2; 3 4]> gap> m[1,2]; 2 gap> - m; <Julia: [-1 -2; -3 -4]> gap> m + m; <Julia: [2 4; 6 8]>
In a Julia session, one can ask for help about the object with the name obj (a function or a type) by entering ?obj, and Julia prints all matches to the screen. One can get the same output in a GAP session by entering ?Julia:obj, cf. Section Reference: Invoking the Help in the GAP Reference Manual. For example, ?Julia:sqrt shows the Julia help about the Julia function sqrt (which is available in GAP as Julia.sqrt).
Note that this way to access the Julia help is different from the usual access to GAP help books, in the following sense.
The qualifying prefix Julia: is mandatory. Thus the help request ?sqrt will show matches from usual GAP help books (there is one match in the GAP Reference Manual), but not the help about the Julia function sqrt.
Since the prefix Julia: does not belong to a preprocessed
help book with chapters, sections, index, etc., help requests of the kinds ?<, ?<<, ?>, ?>> are not meaningful when the previous help request had the prefix ?Julia:. (Also requests with the prefix ??Julia: do not work, but this holds also for usual GAP help books.)
The Julia help system is case sensitive. Thus ?Julia:sqrt yields a match but ?Julia:Sqrt does not, and ?Julia:Set yields a match but ?Julia:set does not.
The Julia help system does currently not support menus in case of multiple matches, all matches are shown at once, and this happens also in a GAP session.
No PDF or HTML version of the Julia help is supported in GAP, only the text format can be shown on the screen. Thus it does not make sense to change the help viewer, cf. Section Reference: Changing the Help Viewer in the GAP Reference Manual.
Julia functions belong to Julia modules. Many Julia functions can be accessed only relative to their modules, and then also the help requests work only for the qualified names. For example, ?Julia:GAP.julia_to_gap yields the description of the Julia function julia_to_gap that is defined in the Julia module GAP, whereas no match is found for the input ?Julia:julia_to_gap.
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