HLASM Lexer — Column-Aware Syntax Highlighting for Notepad++

A Notepad++ plugin that provides column-aware syntax highlighting for IBM High Level Assembler (HLASM) source files. Unlike generic assembly highlighters, this plugin understands the 80-column punch card layout that HLASM requires.

What It Does

HLASM source follows a rigid column layout inherited from 80-column punch cards:

Columns 1-71     Content area (label, operation, operand, remarks)
Column  72       Continuation marker (non-blank = line continues)
Columns 73-80    Sequence number

This plugin highlights each field by its column position, not just by keywords:

Field	Colour	Description
Label	Dark blue, bold	Symbols starting in column 1
Operation	Blue	Instruction/directive after label
Operand	Black	Arguments to the operation
Remarks	Green, italic	Comments after the operand field
String	Red	Quoted constants (C'HELLO', X'FF')
Number	Orange	Numeric literals
Register	Purple	R0–R15
Continuation	Grey on yellow	Non-blank character in column 72
Sequence	Light grey	Columns 73–80
Comment	Green, italic	Lines starting with * or .*

Vertical column ruler lines are drawn at the content/continuation boundary (col 72), continuation/sequence boundary (col 73), and end of card (col 80).

Supported Features

• Full-line comments (* in column 1, .* for macro comments)
• Continuation lines (non-blank in column 72, operand resumes at column 16)
• Multi-line string continuation (tracks open quotes across continuation lines)
• Type-prefixed string constants (C'...', X'...', B'...', F'...', etc.)
• Parenthesised sub-expressions in operands (e.g. AIF ('&REG' EQ '').NOREG)
• Macro variable references (&VAR) and sequence symbols (.LABEL)
• Register detection (R0–R15, case-insensitive)
• Debounced re-styling on edit (50ms delay so typing stays responsive)

Installation

Requirements

• Notepad++ 8.x (64-bit)
• The plugin DLL must match your Notepad++ architecture (64-bit NP++ needs 64-bit DLL)

Steps

1. Close Notepad++ completely.

2. Copy the DLL to the Notepad++ plugins directory:

   C:\Program Files\Notepad++\plugins\HLASMLexer\HLASMLexer.dll
   

   Create the HLASMLexer folder if it doesn't exist. The folder name must match the DLL name (minus the .dll).

3. Restart Notepad++. You should see Plugins → HLASM Lexer → Apply HLASM Highlighting in the menu.

4. Open an HLASM source file and the highlighting applies automatically.

File Extensions

The plugin applies automatically to all files when a buffer is opened. For best results, use one of these extensions for your HLASM source:

Extension	Use
.mlc	Main assembler source (recommended)
.mac	Macro definitions
.cpy	Copy members

!!!!!!! Important: Avoid .asm for HLASM files.

Notepad++ has a built-in Assembly language definition that claims .asm files. Its highlighter will fight with this plugin, producing garbled colours. Rename your files to .mlc or .mac instead. If you must use .asm, go to Settings → Style Configurator → Language: Assembly and remove asm from the file extensions list.

Manual Apply

If auto-apply doesn't trigger for a particular file, use Plugins → HLASM Lexer → Apply HLASM Highlighting from the menu.

Building from Source

Requirements

• MinGW-w64 (64-bit GCC for Windows)
• No other dependencies

Build

g++ -c -Wall -Wextra -O2 -std=c++11 -DUNICODE -D_UNICODE -o obj\hlasm_lexer.o src\hlasm_lexer.cpp
g++ -shared -static -o bin\HLASMLexer.dll obj\hlasm_lexer.o exports.def -s -luser32

Or just run build.bat.

The resulting DLL is ~24KB.

Limitations

• No keyword colouring. Operations like MVC, LA, STM are all the same blue. The plugin highlights by column position, not by matching instruction mnemonics against a dictionary.
• No semantic analysis. The parser doesn't know the difference between a DC operand and a macro parameter, it just follows the column rules.
• Fixed-point and bit-level constructs (e.g. POS, scaled fixed-point) are not specially handled.
• .asm extension conflict. See the installation note above.
• Applies to all buffers. The plugin styles whatever file is open. For non-HLASM files, Notepad++'s built-in lexer will typically override it. If a non-HLASM file looks wrong, just switch to its correct language via the Language menu.
• Full re-style on edit. Every keystroke triggers a full document re-style (debounced to 50ms). This is fine for typical HLASM files (< 5,000 lines) but may lag on very large files.

Architecture

The plugin is a single C++ file (~280 lines) that:

1. Exports the six functions Notepad++ requires from a plugin DLL
2. On buffer activation, reads each line via SCI_GETLINE
3. Parses HLASM column layout into a style byte array
4. Applies styles via SCI_STARTSTYLING + SCI_SETSTYLING
5. Configures colours via SCI_STYLESETFORE / SCI_STYLESETBOLD / etc.
6. Draws column rulers via SCI_MULTIEDGEADDLINE

No custom Scintilla lexer (ILexer5) is used. All interaction with Scintilla is through SendMessage, which avoids cross-compiler ABI issues between MinGW and Notepad++'s MSVC-compiled Scintilla. Yes this was a joy to figure out originally lol!

Licence

Apache 2.0 — see LICENSE.