millfork/docs/lang/literals.md

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Literals and initializers

Numeric literals

Decimal: 1, 10

Binary: %0101, 0b101001

Quaternary: 0q2131

Octal: 0o172

Hexadecimal: $D323, 0x2a2

String literals

String literals are surrounded with double quotes and optionally followed by the name of the encoding:

"this is a string" ascii
"this is also a string"

Characters between the quotes are interpreted literally, there are no ways to escape special characters or quotes.

In some encodings, multiple characters are mapped to the same byte value, for compatibility with multiple variants.

Currently available encodings:

• default – default console encoding (can be omitted)

• scr – default screencodes (usually the same as default, a notable exception are the Commodore computers)

• ascii – standard ASCII

• pet or petscii – PETSCII (ASCII-like character set used by Commodore machines)

• cbmscr or petscr – Commodore screencodes

• apple2 – Apple II charset ($A0–$FE)

• bbc – BBC Micro and ZX Spectrum character set

• jis or jisx – JIS X 0201

• iso_de, iso_no, iso_se, iso_yu – various variants of ISO/IEC-646

• iso_dk, iso_fi – aliases for iso_no and iso_se respectively

When programming for Commodore, use pet for strings you're printing using standard I/O routines and petscr for strings you're copying to screen memory directly.

If the characters in the literal cannot be encoded in particular encoding, an error is raised. However, if the command-line option -flenient-encoding is used, then literals using default and scr encodings replace unsupported characters with supported ones and a warning is issued. For example, if -flenient-encoding is enabled, then a literal "£¥↑ž©ß" is equivalent to:

• "£Y↑z(C)ss" if the default encoding is pet

• "£Y↑z©ss" if the default encoding is bbc

• "?Y^z(C)ss" if the default encoding is ascii

• "?Y^ž(C)ss" if the default encoding is iso_yu

• "?Y^z(C)ß" if the default encoding is iso_de

• "?¥^z(C)ss" if the default encoding is jisx

Note that the final length of the string may vary.

Character literals

Character literals are surrounded by single quotes and optionally followed by the name of the encoding:

'x' ascii
'W'

From the type system point of view, they are constants of type byte.

If the characters in the literal cannot be encoded in particular encoding, an error is raised. However, if the command-line option -flenient-encoding is used, then literals using default and scr encodings replace unsupported characters with supported ones. If the replacement is one characacter long, only a warning is issued, otherwise an error is raised.

Array initialisers

An array is initialized with either:

• a string literal

• a file expression

• a for-style expression

• a format, followed by an array initializer:

  • @word (=@word_le): for every term of the array initializer, emit two bytes, first being the low byte of the value, second being the high byte:
    @word [$1122] is equivalent to [$22, $11]

  • @word_be – like the above, but opposite:
    @word_be [$1122] is equivalent to [$11, $22]

• a list of byte literals and/or other array initializers, surrounded by brackets:

  array a = [1, 2] array b = "----" scr array c = ["hello world!" ascii, 13] array d = file("d.bin") array e = file("d.bin", 128, 256) array f = for x,0,until,8 [x * 3 + 5] // equivalent to [5, 8, 11, 14, 17, 20, 23, 26]

Trailing commas ([1, 2,]) are not allowed.

The parameters for file are: file path, optional start offset, optional length (start offset and length have to be either both present or both absent).

The for-style expression has a variable, a starting index, a direction, a final index, and a parameterizable array initializer. The initializer is repeated for every value of the variable in the given range.