Get a list of variables in a given expression

This code should work if the expression only contains lambda forms. If you use any syntax forms or macros, it may misinterpret symbols which are implicitly quoted as variables. For normal arithmetic expressions it will work fine though - it's only if you include things like ->,~> let, procedure, ' and so on that it will give the wrong result (it would add quite a bit of complexity to handle all of those).

/* abVarsUsed.il

Author     A.D.Beckett
Group      Custom IC (UK), Cadence Design Systems Ltd.
Language   SKILL
Date       Dec 09, 2011 
Modified   
By         

Examples of usage:

> abVarsUsed("1+2*(a+3*b)")
(b a)
> abVarsUsed("a+b+c+d*e+expt(f g)")
(g f e d c b a)

***************************************************

SCCS Info: @(#) abVarsUsed.il 12/09/11.09:10:28 1.1

*/

/***************************************************************
*                                                              *
*              abVarsUsed(expression [varsUsed])               *
*                                                              *
* When called with an expression in a string or list, returns  *
*  a list of the variable names used in the expression. Makes  *
*    the assumption that all functions are lambda functions    *
*                                                              *
***************************************************************/

procedure(abVarsUsed(expression @optional varsUsed)
    case(type(expression) 
        (string
            foreach(subExpr linereadstring(expression)
                varsUsed=abVarsUsed(subExpr varsUsed)
            )
        )
        (list
            ;------------------------------------------------------------
            ; ignore the car of the list because that's the
            ; function name
            ;------------------------------------------------------------
            foreach(elem cdr(expression)
                case(type(elem)
                    (symbol
                        unless(member(elem varsUsed)
                            varsUsed=cons(elem varsUsed)
                        )
                    )
                    (list
                        varsUsed=abVarsUsed(elem varsUsed)
                    )
                )
            )
        )
        (t
            (error "abVarsUsed: expecting string or list: %L\n" expression)
        )
    )
    varsUsed
)

Regards,

Andrew

This code should work if the expression only contains lambda forms. If you use any syntax forms or macros, it may misinterpret symbols which are implicitly quoted as variables. For normal arithmetic expressions it will work fine though - it's only if you include things like ->,~> let, procedure, ' and so on that it will give the wrong result (it would add quite a bit of complexity to handle all of those).

/* abVarsUsed.il

Author     A.D.Beckett
Group      Custom IC (UK), Cadence Design Systems Ltd.
Language   SKILL
Date       Dec 09, 2011 
Modified   
By         

Examples of usage:

> abVarsUsed("1+2*(a+3*b)")
(b a)
> abVarsUsed("a+b+c+d*e+expt(f g)")
(g f e d c b a)

***************************************************

SCCS Info: @(#) abVarsUsed.il 12/09/11.09:10:28 1.1

*/

/***************************************************************
*                                                              *
*              abVarsUsed(expression [varsUsed])               *
*                                                              *
* When called with an expression in a string or list, returns  *
*  a list of the variable names used in the expression. Makes  *
*    the assumption that all functions are lambda functions    *
*                                                              *
***************************************************************/

procedure(abVarsUsed(expression @optional varsUsed)
    case(type(expression) 
        (string
            foreach(subExpr linereadstring(expression)
                varsUsed=abVarsUsed(subExpr varsUsed)
            )
        )
        (list
            ;------------------------------------------------------------
            ; ignore the car of the list because that's the
            ; function name
            ;------------------------------------------------------------
            foreach(elem cdr(expression)
                case(type(elem)
                    (symbol
                        unless(member(elem varsUsed)
                            varsUsed=cons(elem varsUsed)
                        )
                    )
                    (list
                        varsUsed=abVarsUsed(elem varsUsed)
                    )
                )
            )
        )
        (t
            (error "abVarsUsed: expecting string or list: %L\n" expression)
        )
    )
    varsUsed
)

Regards,

Andrew