Build a string representing a complete STEP file from a header and a list of entities. Entities will be assigned integer IDs automatically, and nested entities (entities that reference other entities) will be 'flattened' into separate entities referring to each other by their automatically-generated IDs.

Note that it is not actually necessary to list all entities explicitly, only top-level ones; any entities that are referenced by entities in the given list will also get included in the output.

A Header represents the data stored in the header section of a STEP file:

• fileDescription should be an informal description of the contents of the file.
• fileName may be the file name of the actual file, or it may be an abstract name for the contents of the file used when cross-referencing between files.
• timeStamp should be an ISO 8601-formatted date and time.
• author should include the name and address of the person who created the file.
• organization should be the organization that the author is associated with.
• One of preprocessorVersion or originatingSystem should identify what CAD program was used to generate the file. This does not seem to be used terribly consistently!
• authorization should include the name and address of whoever authorized sending the file.
• schemaIdentifiers identifies the EXPRESS schema used by entities in the file. This will usually be a list containing a single string, which may be either a simple string like "IFC2X3" or an 'object identifier' such as "AUTOMOTIVE_DESIGN { 1 0 10303 214 1 1 1 1 }" (more commonly known as AP214).

An Entity represents a single entity stored in the data section of a STEP file. An entity may be a point, a curve, a part, an assembly, or even an entire building. Every entity has a type and a list of attributes (which can themselves be references to other entities).

Construct a single entity with the given type and attributes. The type name will be capitalized if necessary. An IfcDirection representing the positive Y direction in 3D could be created using

direction =
    Step.entity "IFCDIRECTION"
        [ Step.list Step.float [ 0, 1, 0 ]
        ]

which might get encoded as #1=IFCDIRECTION((0.,1.,0.));.

If a given entity is only referred to by a single other entity, you can create it directly inside the definition of the parent entity. For example, to create entity #121 from this AP214 example, you could use

Step.entity "AXIS2_PLACEMENT_3D"
    [ Step.string ""
    , Step.referenceTo <|
        Step.entity "CARTESIAN_POINT"
            [ Step.list Step.float [ 20, 7.5, 0 ]
            ]
    , Step.referenceTo <|
        Step.entity "DIRECTION"
            [ Step.string ""
            , Step.list Step.float [ 1, 0, 0 ]
            ]
    , Step.referenceTo <|
        Step.entity "DIRECTION"
            [ Step.string ""
            , Step.list Step.float [ 0, 0, -1 ]
            ]
    ]

When actually encoded to a STEP file, this will get converted into four separate entities, with the top-level entity referring to the other three by their automatically-generated IDs, something like:

#1=AXIS2_PLACEMENT_3D('',#2,#3,#4);
#2=CARTESIAN_POINT('',(20.,7.5,0.));
#3=DIRECTION('',(1.,0.,0.));
#4=DIRECTION('',(0.,0.,-1.));

An Attribute represents a single attribute of an Entity, such as an X coordinate value, a GUID string, or a reference to another entity.

The special 'default value' attribute (* in the resulting STEP file).

The special 'null value' attribute ($ in the resulting STEP file).

Construct an integer-valued attribute.

Construct a real-valued attribute.

Construct a string-valued attribute. Unicode characters will be properly escaped according to the (weird, custom) method specified in the STEP standard; for example,

Step.string "see § 4.1"

will end up being encoded as

'see \X\A7 4.1'

Construct a reference to another STEP entity (will end up being encoded using an integer ID in the resulting STEP file, e.g. #123).

Construct an attribute that refers to an enumeration value defined in an EXPRESS schema. Enumeration values are always encoded as all-caps with leading and trailing periods, like .STEEL..

This function will capitalize and add periods if necessary, so both Step.enum "steel" and Step.enum ".STEEL." will be encoded as .STEEL..

Construct a binary-valued attribute. The provided string is assumed to already be hex encoded as required by the STEP standard.

Construct an attribute which is itself a list of other attributes. You provide a list of values and a function to convert each of those values to an attribute (which will usually be one of the attribute construction functions in this module!). For example, to construct an attribute which is a list of floats:

Step.list Step.float [ 0, 1, 0 ]

To construct a list of references to various entities:

Step.list Step.referenceTo
    [ firstEntity
    , secondEntity
    , thirdEntity
    ]

In the odd case where you already have a List Attribute, you can use Elm's built-in identity function as the first argument:

Step.list identity
    [ firstAttribute
    , secondAttribute
    , thirdAttribute
    ]

Construct a type-tagged integer-valued attribute.

Construct a type-tagged float-valued attribute.

Construct a type-tagged string-valued attribute.

Construct a type-tagged enumeration attribute.

Construct a type-tagged binary-valued attribute.

Construct a type-tagged list attribute.