Literals¶

All literal forms that ExpressLexer can emit, with the token they produce.

Strings¶

A simple string is single-quoted; a doubled quote '' escapes a quote inside it (clause 7.5.4):

strings

s1 : STRING := 'hello';
s2 : STRING := 'it''s here';
s3 : STRING := 'a simple string';

Encoded string literal¶

A double-quoted hex string is an encoded (hexadecimal) string literal. Each character is encoded as four octets — the ISO/IEC 10646 group, plane, row and cell — so the hexadecimal digits always come in groups of eight:

encoded string literal

e1 : STRING := "000000E9";             -- one character
e2 : STRING := "00000041000000E9";     -- two characters
e3 : STRING := "1F2A3B";               -- not valid: a group is eight digits

The lexer colours e3 as a string literal all the same: it renders the language rather than validating it, and a partial group is still read as a hexadecimal string. ISO 10303-11 clause 7.5.4, example 4, treats that literal as invalid, so a validator should reject it.

Binary literal¶

A % followed by binary digits:

binary literal

b1 : BINARY := %10110;
b2 : BINARY := %0;
b3 : BINARY := %11111111;

Numbers¶

integers and reals

i1 : INTEGER := 42;
i2 : INTEGER := 0;
r1 : REAL := 3.14;
r2 : REAL := 1.5E-3;
r3 : REAL := 2.0E+10;
r4 : REAL := 1.;          -- trailing dot after the integer part

The E/e exponent, +/- signs and % prefix are all handled by the number and binary rules.