PILOT programming language

A line of PILOT code contains (from left to right) the following syntax elements:

• an optional label
• a command letter
• an optional Y (for yes) or N (for no)
• an optional conditional expression in parentheses
• a colon (":")
• an operand, or multiple operands delimited by commas.

A label can also be alone in a line, not followed by other code. The syntax for a label is an asterisk followed by an identifier (alphanumeric string with alphabetic initial character).

The command letters used in Pilot are as follows:

A:

Accept input into "accept buffer".

Examples:

R:Next line of input replaces current contents of accept buffer A:

R:Next line of input replaces accept buffer, and string variable 'FREE' A:$FREE

R:Next 3 lines of input assigned to string variables 'X', 'Y' and 'Z' A:$X,$Y,$Z

R:Numeric input assigned to numeric variable "Q" A:#Q

C:

Compute and assign numeric value.

Example:

R:Assign arithmetic mean of #X and #Y to #AM C:#AM=(#X+#Y)/2

Most Pilot implementations have only integer arithmetic, and no arrays.

D:

Dimension an array, on some implementations.

E:

End (return from) subroutine. Always used without any operand.

J:

Jump to label.

Example:

J:*RESTART

M:

Match the accept buffer against string variables or literals[?].

Example:

A:Search accept buffer for "TRUTH", the value of $MEXICO and "YOUTH", in that order M:TRUTH,$MEXICO,YOUTH

The first match string (if any) that is a substring of the accept buffer is assigned to the special variable $MATCH. The buffer characters left of the first match are assigned to $LEFT, and the characters on the right are assigned to $RIGHT.

The match flag is set to 'yes' or 'no', depending on whether a match is made. Any statement that has a Y following the command letter is processed only if the match flag is set. Statements with N are processed only if the flag is not set.

N:

Equivalent to TN: (type if last match unsuccessful)

R:

The operand of R: is a comment, and therefore not processed.

T:

'Type' operand as output.

Examples:

R:Output a literal string T:Thank you for your support.

R:Output a variable expression T:Thank you, $NAME.

U:

Use (call) a subroutine. A subroutine starts with a label and ends with E:

Example:

R:Call subroutine starting at label *INITIALIZE U:*INITIALIZE

Y:

Equivalent to TY: (type if last match successful)

If there is parenthesized expression in a statement, it is a test expression[?], and the statement is processed only if the test has a value of 'true'.

Example:

R:Type message if x>y+z T(#X>#Y+#Z):Condition met

The above is a description (but not a definition) of "core pilot". Extensions to core pilot include arrays and floating point numbers in Apple PILOT, and implementation of turtle graphics in Atari PILOT.