Halogen

Halogen is FORTH-like programming language.
(this is a WIP, I might improve this some time later)

Prerequisites

To build Halogen, you need the following utilities:

• GCC (or a similar C compiler)
• GNU Make

Building

To build Halogen, run the following commands:

mkdir bin
make

Note: On some systems (such as BSD), replace make with gmake

Tokens

Halogen scripts go through a process called tokenization, where the script gets broken down into individual tokens. Each token is split up by a space character. There exist multiple types of tokens.

• Words
• Strings
• Numbers
• Word redefinition (:)
• Word redefinition terminator (;)
• Conditional loop (()
• Conditional loop terminator ())
• Comment (#)

Words

Words are commands issued to the interpreter. Their behaviour is defined by the dictionary and can be (re)defined using a word redefinition.

Example: print, swap

Number

A number that gets pushed onto the stack. Can either be decimal or hexadecimal (prefixed with 0x).

Example: 10, 0x3f

String

A sequence of characters that gets pushed onto the stack with the first character on top. The start and end is marked by a double quote ("). To insert a " into a string, use ""

Example: "User data should not be treated as code, even when sanitized", """ <- this will be a single quote"

Word redefinition

A colon followed by the word name. Adds / Changes the specified word in the dictionary. The word redefinition is closed via a redefinition terminator (;).

Example:

:newword
    # Code here #
;

Conditional loop

Loops between ( and ) while the value at the top of the stack is not 0. Note that the value DOES NOT get removed from the stack.

Example:

# Basic for loop #

0 1 (
    pop
    dup print
    1 +
    dup 5 >
)

Comment

Makes interpreter ignore all tokens until the next comment token

Example:

# This is a comment and it shouldn't be treated as code. #