Fifth

ColorFORTH evolved

Fifth is ColorFORTH evolved. Chuck Moore's minimalist language, running on any platform, with optional verification.

Dedication

Fifth is dedicated to Charles H. "Chuck" Moore, creator of Forth (1970) and ColorFORTH (2001).

Chuck's work powers spacecraft, boot firmware, and countless embedded systems. His philosophy — simplicity, directness, minimal abstraction — inspired generations.

Fifth continues the lineage. ColorFORTH semantics, modern platforms, optional verification.

What Evolves

ColorFORTH	Fifth
x86 only	Any GNAT target
No verification	Optional verification
Binary format	Optional text-based source

The minimalism stays.

Toolchain

Fifth compiles to SPARK, then to native machine code via GNAT. This gives you:

Modern platforms — x86-64, ARM64, RISC-V, bare metal
Optional verification — GNATprove proves your code correct
30 years of optimization — GNAT is production-grade

Syntax

Fifth accepts ColorFORTH binary (.cf) or text (.fifth) format.

The .fifth Format

ColorFORTH encodes token type as color. The .fifth format represents these colors as emoji squares (no cyan square exists, so comments use 💬):

🟥 square 🟩 dup * ;
⬜ 5 🟨 square 💬 result: 25

Space after each color marker. Color persists until the next marker.

Emoji	Color	Meaning
🟥	Red	Define word
🟨	Yellow	Execute
🟩	Green	Compile
⬜	White	Number
🟦	Blue	Variable
💬	Cyan	Comment

This is ColorFORTH in Unicode — same semantics, text-serialized.

Optional Verification

Add annotations as comments. Ignored by default, used when verification is requested:

🟥 square 💬 ( n -- n*n )
🟩 dup * ;

This generates SPARK contracts. GNATprove verifies them. If it compiles with verification, your stack effects are proven correct.

Core Words

The full ColorFORTH word set:

Category	Words
Stack	`dup` `drop` `swap` `over` `nip` `push` `pop` `a` `a!`
Arithmetic	`+` `-` `` `/` `/mod` `negate` `2` `2/` `+` `abs` `min` `max`
Logic	`and` `or` `xor` `not`
Comparison	`<` `u<` `0<` `=` `-if`
Memory	`@` `!` `+!` `c@` `c!` `@+` `!+`
Control	`if` `-if` `then` `;` `for` `next` `i` `begin` `while` `until` `jump` `execute`
I/O	`emit` `key` `.` `h.` `cr` `space` `type`
Hardware	`in` `out` `@p` `!p`

Target Platforms

Via GNAT:

x86-64 Linux, Windows
ARM64 Linux, macOS
Bare metal ARM
RISC-V

Space is a separate project — a new language with universes, disciplines, and warps. Fifth is ColorFORTH preserved and modernized. Different goals, shared infrastructure.

The Name

In 1970, Chuck Moore wanted to call his language "Fourth" — a fourth-generation language. The IBM 1130 limited filenames to five characters. "FORTH" it became.

Fifth continues the lineage: Forth → Fourth → Fifth.