Allegro CL Certification Program

Lisp Programming Series Level I

Session 1.1.4

Basic Lisp Development in the IDE

Starting the IDE• From the Windows start menu, start the

development environment

• The windows you get:– Menu bar across the top– Debug window– Untitled Edit window– Form window – Inspect window

Creating a Source File• Find the Edit window (which is initially titled

Untitled)– View > Editor

• Initially, there is a tab named Untitled. (If there is not, create one via File > New.)

• Enter the following source code:(in-package :user)

(defun square (x) (* x x))

– Note the cursors help balance parentheses

Warning

• Put all important source code into files

• Don’t type source code into the debug window!– It won’t be saved if you exit Allegro!– Use debug window only for performing small

experiments

Compile Your Code

• Click on the “truck” icon to compile and load the current source file

• OR Click on the (=>) icon to compile the definition under the cursor

Run Your Code• Bring up the Debug window

• Change to the package where the symbols in your application live

• Run the new function

CG-USER(5): (in-package :user)#<The COMMON-LISP-USER package>CL-USER(6): (square 7)49

CL-USER(7):

Debug your code• Type (squar 7) into the debug window

– Function name is intentionally misspelled• Error: attempt to call 'SQUAR' which is an undefined function.

• You can– Invoke Selected Restart

• Pick from a menu of predefined error handlers

– Debug• Starts the Lisp Debugger

– Abort• Exits the debugger and returns you back to the top level• This is the same as the "Return to Top Level" restart

The Lisp Debugger• Click 'Debug' on the error window to get

here

• Button bar across top– Click on the big “X” to get back to top level

• Display area shows call stack– The bottom of the call stack shows the

functions being used by the IDE itself to evaluate the line of code you just typed

• Debug area for evaluating expressions in the current environment

What You Can And Can't Do

• You can see the call stack, including values of all the arguments

• You can to see local variables, given the proper declaration

(defun foo (x) (declare (optimize (debug 3))) (let ((y (cons 2 3))) (cons x y)))

• You can't step line-by-line through your source code

How to Set a Breakpoint

(defun foo (x)

(declare (optimize (debug 3)))

(let ((y (cons 2 3)))

(BREAK)

(cons x y)))

Tracing Function Execution

• Put this in your source file:(defun add (a b) (+ a b))

(defun sum-squares (x y)

(add (* x x) (* y y)))

• Type three things to the debug window:

(trace add)

(trace sum-squares)

(sum-squares 3 4)

Interpreting Trace Output 0[1]: (SUM-SQUARES 3 4) 1[1]: (ADD 9 16) 1[1]: returned 25 0[1]: returned 25

• The first line shows SUM-SQUARES being called with arguments 3 and 4.

• The second line shows that within the scope of SUM-SQUARES, the function ADD is being called with arguments 9 and 16

• The third line shows the function ADD returns the value 25

• The fourth line shows the function SUM-SQUARES returns the value 25

The Lisp Compiler

• (disassemble # 'square)– Shows the assembly instructions generated by the

compiler

• Instructions depend on your OS

• *.fasl files encode this information

• *.lisp files are portable to multiple OS, but not *.fasl files.

Declarations• Data types of variables are not (usually) declared,

e.g.– int a = 0; OR Dim a as Integer

• Data type of function return value is not declared • Arithmetic is generic

– You can add an integer to a double-float

• Compiler doesn’t warn you about data type problems

• You can optionally declare data types to eliminate generic arithmetic and speed things up