MCNP6 syntax highlighting and snippets

An extension providing syntax highlighting and code snippets for MCNP input decks

Cards, keywords, and constants were taken from the MCNPv6.3.0 user manual but is compatible with most version 6.x input files. By default this applies to files with the .i or .ip file extension. The source is available on github.

Note: The default theme colours are not fantastic, but are easily customised with the template here

Syntax highlighting

All the expected syntax rules are implemented for cards, keywords, constants, and comments. Syntax highlighting rules are case insesnitive, and apply across multiple lines where appropriate, such as with the SDEF and FMESH cards seen in the example below.

Highlighting rules are contextualised and will generally not apply to incorrect syntax or invalid states. In the following example:

• Only tallies ending 1-8 are valid, so FC9 is will not be highlighted
• The XYZ geometry constant is only valid for GEOM=, and fails to highlight on OUT=

Note that while this is a useful indication of problems, it guarantees nothing for runtime.

There are plans to implement a fully featured language server with detailed error reporting, linting, etc... but this is not a trivial task and will take time.

Autocomplete code snippets

Lines may be commented out with the usual ctrl+/ shortcut, adding a c to the start of the selected line(s). The typical bracket matching and quotation autocomplete also included.

Code snippets are defined for input cards where appropriate. Simply start typing and hit enter to generate the card with default values. Tab-stops are defined for all snippets, so pressing tab will then cycle through keywords on the card for editing.

For example, selecting ACT from the suggestions,

will generate the following:

For productivity, keywords and values are set to default or a simple hint where ambiguous.

A comprehensive guide for most cards would take up the entire screen. As a compromise, every line simply has a small comment for context. This is still very useful for cards such as PHYS, which are just sets of values.

The template above is far easier than trying to remember whatever "phys:n 100 0 0 j j j 0 -1 j j 1 0 0" means.

Of course, card snippets are fairly subjective in their usefulness. Any feedback on what defaults, flags, or comments should be used for certain cards would be appreciated.

Customising syntax colours

The textmate naming conventions are used for tokenisation to support most themes. MCNP specific syntax highlighting colours are customisable by overwriting the theme in your settings.json.

Click to show example settings.json template

"editor.tokenColorCustomizations": {
"textMateRules": [
        {
            "scope": "comment.line.mcnp",
            "settings": { "foreground": "#676767" }
        },
        {
            "scope": "keyword.cellnumber.mcnp",
            "settings": { "foreground": "#82AAFF" }
        },
        {
            "scope": "constant.numeric.cellmaterial.mcnp",
            "settings": { "foreground": "#E74856" }
        },
        {
            "scope": "constant.numeric.celldensity.mcnp",
            "settings": { "foreground": "#2AB5CA" }
        },
        {
            "scope": "keyword.surfacenumber.mcnp",
            "settings": { "foreground": "#ea82ff" }
        },
        {
            "scope": "constant.language.surfacetype.mcnp",
            "settings": { "foreground": "#4ecc86" }
        },
        {
            "scope": "constant.language.zaidlib.mcnp",
            "settings": { "foreground": "#e88e96" }
        },
        {
            "scope": "keyword.mcnp",
            "settings": { "foreground": "#82AAFF" }
        },
        {
            "scope": "constant.numeric.mcnp",
            "settings": { "foreground": "#B987E1" }
        },
        {
            "scope": "variable.mcnp",
            "settings": { "foreground": "#a3d3fb" }
        },
        {
            "scope": "constant.language.mcnp",
            "settings": { "foreground": "#4ecc86" }
        },
        {
            "scope": "string.mcnp",
            "settings": { "foreground": "#ea6cc7" }  
        }
    ]
}

Click to show table of scopes

Values for the MCNP syntax "scope" are described in the table below.

Syntax description	Example	Scope
Comments	c example comment line	comment.line.mcnp
Cell number	99 5 -0.26 surface numbers...	keyword.cellnumber.mcnp
Cell material number	99 5 -0.26 surface numbers...	constant.numeric.cellmaterial.mcnp
Cell material density	99 5 -0.26 surface numbers...	constant.numeric.celldensity.mcnp
Surface number	20 PX values...	keyword.surfacenumber.mcnp
Surface type	20 PX values...	constant.language.surfacetype.mcnp
ZAID suffix	M1 08016.32c 1.0	constant.language.zaidlib.mcnp
Data card name	fmesh34:n geom=rzt	keyword.mcnp
Numeric identifiers	fmesh34:n geom=rzt	constant.numeric.mcnp
General variable	fmesh34:n geom=rzt	variable.mcnp
General constants	fmesh34:n geom=rzt	constant.language.mcnp
Strings	fc34 example tally comment	string.mcnp

Issues and bugs

It is guaranteed that there are missing cards or rules that are not working as intended, so if you find anything please raise an issue.

Suggestions for improvements and features are also welcome.

Notes for developers

The JSON files quickly spiral out of control with all the nuances of the various input cards and their edge cases.

The YAML file format is much easier to deal with, so it is suggested that you just install js-yaml and convert updates from the YAML versions.

    # Install js-yaml
    $ npm install js-yaml

    # Use the command-line tool to convert the yaml files to json
    $ npx js-yaml syntaxes/mcnp.tmLanguage.yaml > syntaxes/mcnp.tmLanguage.json
    $ npx js-yaml snippets/mcnp.tmSnippets.yaml > snippets/mcnp.tmSnippets.json

The included .vscode/launch.json allows for easy development. Hit F5 to bring up a debug instance with the extension loaded, and ctrl+R to reload the window whenever a change is made.