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• c4a supports control characters in the whitespace that change the state.
  
• c4a has 4 states: INTERPRET, COMPILE, DEFINE, AND COMMENT,
  
• c4a also supports the standard state-change words.
  

NOTE: In the DEFINE state, c4a changes the state to COMPILE after adding the next word.
NOTE: Unlike ColorForth, ';' compiles EXIT and then changes the state to INTERPRET.

• In c4a, a program is a sequence of WORD-CODEs.
  
• A WORD-CODE is a 16-bit unsigned number.
  
• Primitives are assigned numbers sequentially from 0 to [BYE].
  
• If a WORD-CODE is less than or equal to [BYE], it is a primitive.
  
• If the top 3 bits are set, it is 13-bit unsigned literal, 0-$1FFF.
  
• If it is between [BYE], and $E000, it is the code address of a word to execute.
  

• ACELL in c4a is 32-bits.
• For PCs, only 32-bit platforms are supported.
• For 64-bit systems, see c4:https://github.com/CCurl/c4.

• Windows: there is a c4a.sln file for Visual Studio
  • only the x86 target is supported
• Linux: there is a makefile
  • only the 32-bit configuration (-m32) is supported
• Others:
  • c4a is simple enough that it should be easy to migrate it to any platform

• I use the Arduino IDE v2.x
• There is a c4a.ino file
• Filec4a.h controls parameters for the target board
• Edit the section whereIS_BOARD is defined to set the configuration for the board
• Use#define FILE_NONE to disable support for blocks and LittleFS
• For the RPI Pico:
  • Use the arduino-pico from earlephilhower (https://github.com/earlephilhower/arduino-pico)
  • The version must be 4.2.0 or later. Versions older than 4.0.0 do not support boards usingthe RP2350 microcontroller.
  • Use#define FILE_PICO to include support for LittleFS
• For the Teensy-4.x:
  • Use#define FILE_TEENSY to include support for LittleFS

c4a provides a single memory area. See 'mem-sz' (MEM_SZ in c4a.h) for its size.

• It is broken into 3 areas: CODE, VARS, and DICT.
• The CODE area is an aray of WORD-CODEs starting at the beginning of the memory.
  • here is an offset into the CODE area.
  • The size of the CODE area iscode-sz. See CODE_SZ in c4a.h.
  • NOTE: Usewc@ andwc! to get and set WORD-CODE values in the code area.
  • NOTE: CODE slots 0-25 (0 wc@ .. 25 wc@) are reserved for c4a system values.
  • NOTE: CODE slots 26-[BYE] (26 wc@ ..[BYE] wc@) are unused by c4a.
  • NOTE: So c4a provides space for about 75 'free' 16-bit variables.
  • NOTE: These are free for the user/application to use as desired.
• The VARS area is defined to begin at addresscode-sz wc-sz * memory +.
  • vhere is the absolute address of the first free byte the VARS area.
• The DICT is at the end of the memory. 'last' grows toward the beginning of the memory.
  • last is an offset into the memory area.
• Use->memory to turn an offset into an address.

Strings in c4a are NULL-terminated with no count byte.

Similar to the printf() function in C, c4a supports formatted output using '%'.
For example: ascii dup dup dup ." char: %c, decimal: #%d, binary: %%%b, hex: $%x%n" ;.

c4a includes an A stack.
This is somewhat similar to ColorForth's operations for 'a', but in c4a, it is a stack.
The size of the A stack is configurable (seetstk-sz).

c4a includes a T stack, with the same operations as the A stack.
Note that there are also additional words for the return stack.

c4a provides 10 temporary words, 't0' .. 't9'.

• They are case-sensitive.
• • 'T0' is NOT a temporary word, but 't0' is.
• They do not take valuable dictionary space.
• They can be used to improve factoring, or as variable or constant names.
• They cannot be made IMMEDIATE or INLINE.

Stack effect notation conventions:

The primitives:

Default words are defined in functionsys_load() in file sys-load.cpp.
For details, or to add or change the default words, modify that function.