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environmental-symbols.md

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April APL Environmental Symbols

These symbols represent values defining the environment in which April code runs.

System Variables

These variables can be reassigned by the user; for instance, ⎕io←0 sets the index origin to 0.

Symbol Name Description
⎕IO Index Origin The number from which counting begins; may be 1 (default) or any other non-negative integer.
⎕CT Comparison Tolerance Difference between floating point numbers below which they are considered equal.
⎕PP Print Precision Precision at which decimal values are expressed for printing; default 10.
⎕DIV Division Method Defines how division by 0 is handled; may be 0 (default) or 1.
⎕RL Random Link Assign this variable to set the random number generator and/or seed to use.

April's Unique System Variables

These are system variables exclusive to April, not found in any other variant of APL.

Symbol Name Description
⎕OST Output Stream The Lisp output stream to which formatted console output is sent.

System Constants

The values of these symbols are fixed and cannot be changed.

Symbol Name Description
⎕A Alphabet Vector String of capital letter characters in the English Roman alphabet.
⎕D Digit Vector String of numeric characters from 0 to 9.

System Functions

These symbols represent standard functions available within April. Currently, the only system function is ⎕TS, which takes no arguments and returns a timestamp vector.

Symbol Name Description
⎕TS Timestamp Evaluates to the current APL timestamp: a vector of 7 values expressing year, month, day, hour, minute, second and millisecond.
⎕NS Create Namespace Return an empty namespace.
⎕CS Set Namespace Point Set the starting point for namespace paths within a scope.
⎕UCS Unicode Convert Convert unicode characters into integers and vice versa.
⎕FMT Format Create a character matrix containing the printed representation of an array.

April's Unique System Functions

Symbol Name Description
⎕TY Coerce/Get Type Get enumerated type of an array or coerce an array to an enumerated type.
⎕XWV External Workspace Value Fetch one or more values from another workspace.
⎕XWF External Workspace Function Fetch one or more functions from another workspace.
⎕XWO External Workspace Operator Fetch one or more operators from another workspace.