Expressions (changes)
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Expressions
Sub-expressions should be wrapped in brackets.
eg. (“myfile/doc” RIGHT 4) LEFT 1 = “/”
System variable expansion
Prior to RISC OS 5.29, 10th February 2021
It was documented that any strings in the expression were passed to OS_GSTrans, to expand system variable and decimal character codes. This would allow testing is a system variable is defined like:
"<Alias$@RunType_FFB>" = ""
However in reality the translation was done to the entire expression before parsing, which would likely result in the above expression being transformed to:
"Basic -quit "%0" %*1" = ""
which would result in an “Unknown operand” error.
After RISC OS 5.29, 10th February 2021
The system variable expansion was modified to a two pass scheme to prevent the value of the system variables expanded in strings being interpreted as expression syntax.
- The unquoted parts of the expression are expanded.
- The expression is parsed.
- The literal strings are expanded.
Operations
Notes
- Keywords must be UPPERCASE
- n stands for an integer value
- s stands for a string value
- a stands for anything (integer or string)
- A space is advised after the < and << operators to prevent confusion with system variable expansion, especially before RISC OS 5.21.
Arithmetic
- n + n Integer addition
- n – n Integer subtraction
- n * n Integer multiplication
- n / n Integer division
- n MOD n Modulo division (i.e. remainder)
Boolean
- n << n Logical shift left
- n >> n Arithmetic shift right
- n >>> n Logical shift right
- n AND n And
- n OR n Or
- n EOR n Exclusive or
- n NOT n Not
String
- s + s Concatenation
- s LEFT n Leftmost characters
- s RIGHT n Rightmost characters
- LEN s Number of characters
Comparison (-1 is TRUE, 0 is FALSE)
- a = a Equal
- a <> a Not equal
- a < a Less than
- a > a Greater than
- a <= a Less than or equal
- a >= a Greater than or equal
Conversion
- STR n From integer to string
- VAL s From string to integer
See also
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