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# 40. Function Definition

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## 40.1 Introduction to Function Definition

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## 40.2 Function

To define a function in Maxima you use the := operator. E.g.

    f(x) := sin(x)

defines a function `f`. Anonmyous functions may also be created using `lambda`. For example

    lambda ([i, j], ...)

can be used instead of `f` where

    f(i,j) := block ([], ...);
    map (lambda ([i], i+1), l)

would return a list with 1 added to each term.

You may also define a function with a variable number of arguments, by having a final argument which is assigned to a list of the extra arguments:

    (%i1) f ([u]) := u;
    (%o1)                      f([u]) := u
    (%i2) f (1, 2, 3, 4);
    (%o2)                     [1, 2, 3, 4]
    (%i3) f (a, b, [u]) := [a, b, u];
    (%o3)               f(a, b, [u]) := [a, b, u]
    (%i4) f (1, 2, 3, 4, 5, 6);
    (%o4)                 [1, 2, [3, 4, 5, 6]]

The right hand side of a function is an expression. Thus if you want a sequence of expressions, you do

    f(x) := (expr1, expr2, ...., exprn);

and the value of exprn is what is returned by the function.

If you wish to make a `return` from some expression inside the function then you must use `block` and `return`.

    block ([], expr1, ..., if (a > 10) then return(a), ..., exprn)

is itself an expression, and so could take the place of the right hand side of a function definition. Here it may happen that the return happens earlier than the last expression.

The first `[]` in the block, may contain a list of variables and variable assignments, such as `[a: 3, b, c: []]`, which would cause the three variables `a`,`b`,and `c` to not refer to their global values, but rather have these special values for as long as the code executes inside the `block`, or inside functions called from inside the `block`. This is called dynamic binding, since the variables last from the start of the block to the time it exits. Once you return from the `block`, or throw out of it, the old values (if any) of the variables will be restored. It is certainly a good idea to protect your variables in this way. Note that the assignments in the block variables, are done in parallel. This means, that if you had used `c: a` in the above, the value of `c` would have been the value of `a` at the time you just entered the block, but before `a` was bound. Thus doing something like

    block ([a: a], expr1, ... a: a+3, ..., exprn)

will protect the external value of `a` from being altered, but would let you access what that value was. Thus the right hand side of the assignments, is evaluated in the entering context, before any binding occurs. Using just `block ([x], ...` would cause the `x` to have itself as value, just as if it would have if you entered a fresh Maxima session.

The actual arguments to a function are treated in exactly same way as the variables in a block. Thus in

    f(x) := (expr1, ..., exprn);

and

    f(1);

we would have a similar context for evaluation of the expressions as if we had done

    block ([x: 1], expr1, ..., exprn)

Inside functions, when the right hand side of a definition, may be computed at runtime, it is useful to use `define` and possibly `buildq`.

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## 40.3 Macros

Function: buildq (L, expr)

  Substitutes variables named by the list L into the expression expr, in parallel, without evaluating expr. The resulting expression is simplified, but not evaluated, after `buildq` carries out the substitution.

  The elements of L are symbols or assignment expressions `symbol: value`, evaluated in parallel. That is, the binding of a variable on the right-hand side of an assignment is the binding of that variable in the context from which `buildq` was called, not the binding of that variable in the variable list L. If some variable in L is not given an explicit assignment, its binding in `buildq` is the same as in the context from which `buildq` was called.

  Then the variables named by L are substituted into expr in parallel. That is, the substitution for every variable is determined before any substitution is made, so the substitution for one variable has no effect on any other.

  If any variable x appears as `splice (x)` in expr, then x must be bound to a list, and the list is spliced (interpolated) into expr instead of substituted.

  Any variables in expr not appearing in L are carried into the result verbatim, even if they have bindings in the context from which `buildq` was called.

  Examples

  `a` is explicitly bound to `x`, while `b` has the same binding (namely 29) as in the calling context, and `c` is carried through verbatim. The resulting expression is not evaluated until the explicit evaluation `''%`.

      (%i1) (a: 17, b: 29, c: 1729)$
      (%i2) buildq ([a: x, b], a + b + c);
      (%o2)                      x + c + 29
      (%i3) ''%;
      (%o3)                       x + 1758

  `e` is bound to a list, which appears as such in the arguments of `foo`, and interpolated into the arguments of `bar`.

      (%i1) buildq ([e: [a, b, c]], foo (x, e, y));
      (%o1)                 foo(x, [a, b, c], y)
      (%i2) buildq ([e: [a, b, c]], bar (x, splice (e), y));
      (%o2)                  bar(x, a, b, c, y)

  The result is simplified after substitution. If simplification were applied before substitution, these two results would be the same.

      (%i1) buildq ([e: [a, b, c]], splice (e) + splice (e));
      (%o1)                    2 c + 2 b + 2 a
      (%i2) buildq ([e: [a, b, c]], 2 * splice (e));
      (%o2)                        2 a b c

  The variables in L are bound in parallel; if bound sequentially, the first result would be `foo (b, b)`. Substitutions are carried out in parallel; compare the second result with the result of `subst`, which carries out substitutions sequentially.

      (%i1) buildq ([a: b, b: a], foo (a, b));
      (%o1)                       foo(b, a)
      (%i2) buildq ([u: v, v: w, w: x, x: y, y: z, z: u], bar (u, v, w, x, y, z));
      (%o2)                 bar(v, w, x, y, z, u)
      (%i3) subst ([u=v, v=w, w=x, x=y, y=z, z=u], bar (u, v, w, x, y, z));
      (%o3)                 bar(u, u, u, u, u, u)

  Construct a list of equations with some variables or expressions on the left-hand side and their values on the right-hand side. `macroexpand` shows the expression returned by `show_values`.

      (%i1) show_values ([L]) ::= buildq ([L], map ("=", 'L, L));
      (%o1)   show_values([L]) ::= buildq([L], map("=", 'L, L))
      (%i2) (a: 17, b: 29, c: 1729)$
      (%i3) show_values (a, b, c - a - b);
      (%o3)              [a = 17, b = 29, c = 1729]

Function: macroexpand (expr)

  Returns the macro expansion of expr without evaluating it, when `expr` is a macro function call. Otherwise, `macroexpand` returns expr.

  If the expansion of expr yields another macro function call, that macro function call is also expanded.

  `macroexpand` quotes its argument. However, if the expansion of a macro function call has side effects, those side effects are executed.

  See also `::=`, `macros`, and `macroexpand1`.

  Examples

      (%i1) g (x) ::= x / 99;
                                          x
      (%o1)                      g(x) ::= --
                                          99
      (%i2) h (x) ::= buildq ([x], g (x - a));
      (%o2)            h(x) ::= buildq([x], g(x - a))
      (%i3) a: 1234;
      (%o3)                         1234
      (%i4) macroexpand (h (y));
                                    y - a
      (%o4)                         -----
                                     99
      (%i5) h (y);
                                  y - 1234
      (%o5)                       --------
                                     99

Function: macroexpand1 (expr)

  Returns the macro expansion of expr without evaluating it, when `expr` is a macro function call. Otherwise, `macroexpand1` returns expr.

  `macroexpand1` quotes its argument. However, if the expansion of a macro function call has side effects, those side effects are executed.

  If the expansion of expr yields another macro function call, that macro function call is not expanded.

  See also `::=`, `macros`, and `macroexpand`.

  Examples

      (%i1) g (x) ::= x / 99;
                                          x
      (%o1)                      g(x) ::= --
                                          99
      (%i2) h (x) ::= buildq ([x], g (x - a));
      (%o2)            h(x) ::= buildq([x], g(x - a))
      (%i3) a: 1234;
      (%o3)                         1234
      (%i4) macroexpand1 (h (y));
      (%o4)                       g(y - a)
      (%i5) h (y);
                                  y - 1234
      (%o5)                       --------
                                     99

Global variable: macros

  Default value: `[]`

  `macros` is the list of user-defined macro functions. The macro function definition operator `::=` puts a new macro function onto this list, and `kill`, `remove`, and `remfunction` remove macro functions from the list.

  See also `infolists`.

Function: splice (a)

  Splices (interpolates) the list named by the atom a into an expression, but only if `splice` appears within `buildq`; otherwise, `splice` is treated as an undefined function. If appearing within `buildq` as a alone (without `splice`), a is substituted (not interpolated) as a list into the result. The argument of `splice` can only be an atom; it cannot be a literal list or an expression which yields a list.

  Typically `splice` supplies the arguments for a function or operator. For a function `f`, the expression `f (splice (a))` within `buildq` expands to `f (a[1], a[2], a[3], ...)`. For an operator `o`, the expression `"o" (splice (a)` within `buildq` expands to `"o" (a[1], a[2], a[3], ...)`, where `o` may be any type of operator (typically one which takes multiple arguments). Note that the operator must be enclosed in double quotes `"`.

  Examples

      (%i1) buildq ([x: [1, %pi, z - y]], foo (splice (x)) / length (x));
                             foo(1, %pi, z - y)
      (%o1)                -----------------------
                           length([1, %pi, z - y])
      (%i2) buildq ([x: [1, %pi]], "/" (splice (x)));
                                      1
      (%o2)                          ---
                                     %pi
      (%i3) matchfix ("<>", "<>");
      (%o3)                          <>
      (%i4) buildq ([x: [1, %pi, z - y]], "<>" (splice (x)));
      (%o4)                   <>1, %pi, z - y<>

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## 40.4 Definitions for Function Definition

Function: apply (f, [x_1, ..., x_n])

  Returns the result of applying the function f to the list of arguments x_1, ..., x_n. f is the name of a function or a lambda expression.

  This is useful when it is desired to compute the arguments to a function before applying that function. For example, if `l` is the list `[1, 5, -10.2, 4, 3]`, then `apply (min, l)` gives -10.2. `apply` is also useful when calling functions which do not have their arguments evaluated if it is desired to cause evaluation of them. For example, if `filespec` is a variable bound to the list `[test, case]` then `apply (closefile, filespec)` is equivalent to `closefile (test, case)`. In general the first argument to `apply` should be preceded by a ' to make it evaluate to itself. Since some atomic variables have the same name as certain functions the values of the variable would be used rather than the function because `apply` has its first argument evaluated as well as its second.

Function: block ([v_1, ..., v_m], expr_1, ..., expr_n)
Function: block (expr_1, ..., expr_n)

  `block` evaluates expr_1, ..., expr_n in sequence and returns the value of the last expression evaluated. The sequence can be modified by the `go`, `throw`, and `return` functions. The last expression is expr_n unless `return` or an expression containing `throw` is evaluated. Some variables v_1, ..., v_m can be declared local to the block; these are distinguished from global variables of the same names. If no variables are declared local then the list may be omitted. Within the block, any variable other than v_1, ..., v_m is a global variable.

  `block` saves the current values of the variables v_1, ..., v_m (if any) upon entry to the block, then unbinds the variables so that they evaluate to themselves. The local variables may be bound to arbitrary values within the block but when the block is exited the saved values are restored, and the values assigned within the block are lost.

  `block` may appear within another `block`. Local variables are established each time a new `block` is evaluated. Local variables appear to be global to any enclosed blocks. If a variable is non-local in a block, its value is the value most recently assigned by an enclosing block, if any, otherwise, it is the value of the variable in the global environment. This policy may coincide with the usual understanding of "dynamic scope".

  If it is desired to save and restore other local properties besides `value`, for example `array` (except for complete arrays), `function`, `dependencies`, `atvalue`, `matchdeclare`, `atomgrad`, `constant`, and `nonscalar` then the function `local` should be used inside of the block with arguments being the names of the variables.

  The value of the block is the value of the last statement or the value of the argument to the function `return` which may be used to exit explicitly from the block. The function `go` may be used to transfer control to the statement of the block that is tagged with the argument to `go`. To tag a statement, precede it by an atomic argument as another statement in the block. For example: `block ([x], x:1, loop, x: x+1, ..., go(loop), ...)`. The argument to `go` must be the name of a tag appearing within the block. One cannot use `go` to transfer to a tag in a block other than the one containing the `go`.

  Blocks typically appear on the right side of a function definition but can be used in other places as well.

Function: break (expr_1, ..., expr_n)

  Evaluates and prints expr_1, ..., expr_n and then causes a Maxima break at which point the user can examine and change his environment. Upon typing `exit;` the computation resumes.

Function: catch (expr_1, ..., expr_n)

  Evaluates expr_1, ..., expr_n one by one; if any leads to the evaluation of an expression of the form `throw (arg)`, then the value of the `catch` is the value of `throw (arg)`, and no further expressions are evaluated. This "non-local return" thus goes through any depth of nesting to the nearest enclosing `catch`. If there is no `catch` enclosing a `throw`, an error message is printed.

  If the evaluation of the arguments does not lead to the evaluation of any `throw` then the value of `catch` is the value of expr_n.

      (%i1) lambda ([x], if x < 0 then throw(x) else f(x))$
      (%i2) g(l) := catch (map (''%, l))$
      (%i3) g ([1, 2, 3, 7]);
      (%o3)               [f(1), f(2), f(3), f(7)]
      (%i4) g ([1, 2, -3, 7]);
      (%o4)                          - 3

  The function `g` returns a list of `f` of each element of `l` if `l` consists only of non-negative numbers; otherwise, `g` "catches" the first negative element of `l` and "throws" it up.

Function: compfile (filename, f_1, ..., f_n)

  Translates Maxima functions f_1, ..., f_n into Lisp and writes the translated code into the file filename.

  The Lisp translations are not evaluated, nor is the output file processed by the Lisp compiler. `translate` creates and evaluates Lisp translations. `compile_file` translates Maxima into Lisp, and then executes the Lisp compiler.

  See also `translate`, `translate_file`, and `compile_file`.

Function: compile (f_1, ..., f_n)
Function: compile (functions)
Function: compile (all)

  Translates Maxima functions f_1, ..., f_n into Lisp, evaluates the Lisp translations, and calls the Lisp function `COMPILE` on each translated function. `compile` returns a list of the names of the compiled functions.

  `compile (all)` or `compile (functions)` compiles all user-defined functions.

  `compile` quotes its arguments; the double-single-quotes operator `''` defeats quotation.

Function: define (f(x_1, ..., x_n), expr)

  Defines a function named f with arguments x_1, ..., x_n and function body expr.

  `define` quotes its first argument in most cases, and evaluates its second argument unless explicitly quoted. However, if the first argument is an expression of the form `ev (expr)`, `funmake (expr)`, or `arraymake (expr)`, the first argument is evaluated; this allows for the function name to be computed, as well as the body.

  `define` is similar to the function definition operator `:=`, but when `define` appears inside a function, the definition is created using the value of `expr` at execution time rather than at the time of definition of the function which contains it.

  All function definitions appear in the same namespace; defining a function `f` within another function `g` does not limit the scope of `f` to `g`.

  Examples:

      (%i1) foo: 2^bar;
                                     bar
      (%o1)                         2
      (%i2) g(x) := (f_1 (y) :=   foo*x*y,
                     f_2 (y) := ''foo*x*y,
             define (f_3 (y),     foo*x*y),
             define (f_4 (y),   ''foo*x*y));
                                                   bar
      (%o2) g(x) := (f_1(y) := foo x y, f_2(y) := 2    x y,
                                                              bar
                     define(f_3(y), foo x y), define(f_4(y), 2    x y))
      (%i3) functions;
      (%o3)                        [g(x)]
      (%i4) g(a);
                                          bar
      (%o4)                  f_4(y) := a 2    y
      (%i5) functions;
      (%o5)        [g(x), f_1(y), f_2(y), f_3(y), f_4(y)]
      (%i6) dispfun (f_1, f_2, f_3, f_4);
      (%t6)                   f_1(y) := foo x y

                                        bar
      (%t7)                  f_2(y) := 2    x y

                                          bar
      (%t8)                  f_3(y) := a 2    y

                                          bar
      (%t9)                  f_4(y) := a 2    y

      (%o9)                         done

Function: define_variable (name, default_value, mode)

  Introduces a global variable into the Maxima environment. `define_variable` is useful in user-written packages, which are often translated or compiled.

  `define_variable` carries out the following steps:

  1. `mode_declare (name, mode)` declares the mode of name to the translator. See `mode_declare` for a list of the possible modes.
  2. If the variable is unbound, default_value is assigned to name.
  3. `declare (name, special)` declares it special.
  4. Associates name with a test function to ensure that name is only assigned values of the declared mode.

  The `value_check` property can be assigned to any variable which has been defined via `define_variable` with a mode other than `any`. The `value_check` property is a lambda expression or the name of a function of one variable, which is called when an attempt is made to assign a value to the variable. The argument of the `value_check` function is the would-be assigned value.

  `define_variable` evaluates `default_value`, and quotes `name` and `mode`. `define_variable` returns the current value of `name`, which is `default_value` if `name` was unbound before, and otherwise it is the previous value of `name`.

  Examples:

  `foo` is a Boolean variable, with the initial value `true`.

      (%i1) define_variable (foo, true, boolean);
      (%o1)                         true
      (%i2) foo;
      (%o2)                         true
      (%i3) foo: false;
      (%o3)                         false
      (%i4) foo: %pi;
      Error: foo was declared mode boolean, has value: %pi
       -- an error.  Quitting.  To debug this try debugmode(true);
      (%i5) foo;
      (%o5)                         false

  `bar` is an integer variable, which must be prime.

      (%i1) define_variable (bar, 2, integer);
      (%o1)                           2
      (%i2) qput (bar, prime_test, value_check);
      (%o2)                      prime_test
      (%i3) prime_test (y) := if not primep(y) then error (y, "is not prime.");
      (%o3) prime_test(y) := if not primep(y)

                                         then error(y, "is not prime.")
      (%i4) bar: 1439;
      (%o4)                         1439
      (%i5) bar: 1440;
      1440 is not prime.
      #0: prime_test(y=1440)
       -- an error.  Quitting.  To debug this try debugmode(true);
      (%i6) bar;
      (%o6)                         1439

  `baz_quux` is a variable which cannot be assigned a value. The mode `any_check` is like `any`, but `any_check` enables the `value_check` mechanism, and `any` does not.

      (%i1) define_variable (baz_quux, 'baz_quux, any_check);
      (%o1)                       baz_quux
      (%i2) F: lambda ([y], if y # 'baz_quux then error ("Cannot assign to `baz_quux'."));
      (%o2) lambda([y], if y # 'baz_quux

                              then error(Cannot assign to `baz_quux'.))
      (%i3) qput (baz_quux, ''F, value_check);
      (%o3) lambda([y], if y # 'baz_quux

                              then error(Cannot assign to `baz_quux'.))
      (%i4) baz_quux: 'baz_quux;
      (%o4)                       baz_quux
      (%i5) baz_quux: sqrt(2);
      Cannot assign to `baz_quux'.
      #0: lambda([y],if y # 'baz_quux then error("Cannot assign to `baz_quux'."))(y=sqrt(2))
       -- an error.  Quitting.  To debug this try debugmode(true);
      (%i6) baz_quux;
      (%o6)                       baz_quux

Function: dispfun (f_1, ..., f_n)
Function: dispfun (all)

  Displays the definition of the user-defined functions f_1, ..., f_n. Each argument may be the name of a macro (defined with `::=`), an ordinary function (defined with `:=` or `define`), an array function (defined with `:=` or `define`, but enclosing arguments in square brackets `[ ]`), a subscripted function, (defined with `:=` or `define`, but enclosing some arguments in square brackets and others in parentheses `( )`) one of a family of subscripted functions selected by a particular subscript value, or a subscripted function defined with a constant subscript.

  `dispfun (all)` displays all user-defined functions as given by the `functions`, `arrays`, and `macros` lists, omitting subscripted functions defined with constant subscripts.

  `dispfun` creates an intermediate expression label (`%t1`, `%t2`, etc.) for each displayed function, and assigns the function definition to the label. In contrast, `fundef` returns the function definition.

  `dispfun` quotes its arguments; the double-single-quote operator `''` defeats quotation. `dispfun` returns the list of intermediate expression labels corresponding to the displayed functions.

  Examples:

      (%i1) m(x, y) ::= x^(-y);
                                           - y
      (%o1)                   m(x, y) ::= x
      (%i2) f(x, y) :=  x^(-y);
                                           - y
      (%o2)                    f(x, y) := x
      (%i3) g[x, y] :=  x^(-y);
                                          - y
      (%o3)                     g     := x
                                 x, y
      (%i4) h[x](y) :=  x^(-y);
                                          - y
      (%o4)                     h (y) := x
                                 x
      (%i5) i[8](y) :=  8^(-y);
                                          - y
      (%o5)                     i (y) := 8
                                 8
      (%i6) dispfun (m, f, g, h, h[5], h[10], i[8]);
                                           - y
      (%t6)                   m(x, y) ::= x

                                           - y
      (%t7)                    f(x, y) := x

                                          - y
      (%t8)                     g     := x
                                 x, y

                                          - y
      (%t9)                     h (y) := x
                                 x

                                          1
      (%t10)                     h (y) := --
                                  5        y
                                          5

                                           1
      (%t11)                    h  (y) := ---
                                 10         y
                                          10

                                          - y
      (%t12)                    i (y) := 8
                                 8

      (%o12)       [%t6, %t7, %t8, %t9, %t10, %t11, %t12]
      (%i12) ''%;
                           - y              - y            - y
      (%o12) [m(x, y) ::= x   , f(x, y) := x   , g     := x   ,
                                                  x, y
                        - y           1              1             - y
              h (y) := x   , h (y) := --, h  (y) := ---, i (y) := 8   ]
               x              5        y   10         y   8
                                      5             10

System variable: functions

  Default value: `[]`

  `functions` is the list of user-defined Maxima functions in the current session. A user-defined function is a function constructed by `define` or `:=`. A function may be defined at the Maxima prompt or in a Maxima file loaded by `load` or `batch`. Lisp functions, however, are not added to `functions`.

Function: fundef (f)

  Returns the definition of the function f.

  The argument may be the name of a macro (defined with `::=`), an ordinary function (defined with `:=` or `define`), an array function (defined with `:=` or `define`, but enclosing arguments in square brackets `[ ]`), a subscripted function, (defined with `:=` or `define`, but enclosing some arguments in square brackets and others in parentheses `( )`) one of a family of subscripted functions selected by a particular subscript value, or a subscripted function defined with a constant subscript.

  `fundef` quotes its argument; the double-single-quote operator `''` defeats quotation.

  `fundef (f)` returns the definition of f. In contrast, `dispfun (f)` creates an intermediate expression label and assigns the definition to the label.

Function: funmake (name, [arg_1, ..., arg_n])

  Returns an expression `name (arg_1, ..., arg_n)`. The return value is simplified, but not evaluated, so the function is not called.

  `funmake` evaluates its arguments.

  Examples:

  - `funmake` evaluates its arguments, but not the return value.

        (%i1) det(a,b,c) := b^2 -4*a*c$
        (%i2) x: 8$
        (%i3) y: 10$
        (%i4) z: 12$
        (%i5) f: det$
        (%i6) funmake (f, [x, y, z]);
        (%o6)                    det(8, 10, 12)
        (%i7) ''%;
        (%o7)                         - 284

  - Maxima simplifies `funmake`'s return value.

        (%i1) funmake (sin, [%pi/2]);
        (%o1)                           1

Function: lambda ([x_1, ..., x_m], expr_1, ..., expr_n)
Function: lambda ([[L]], expr_1, ..., expr_n)
Function: lambda ([x_1, ..., x_m, [L]], expr_1, ..., expr_n)

  Defines and returns a lambda expression (that is, an anonymous function). The function may have required arguments x_1, ..., x_m and/or optional arguments L, which appear within the function body as a list. The return value of the function is expr_n. A lambda expression can be assigned to a variable and evaluated like an ordinary function. A lambda expression may appear in some contexts in which a function name is expected.

  When the function is evaluated, unbound local variables x_1, ..., x_m are created. `lambda` may appear within `block` or another `lambda`; local variables are established each time another `block` or `lambda` is evaluated. Local variables appear to be global to any enclosed `block` or `lambda`. If a variable is not local, its value is the value most recently assigned in an enclosing `block` or `lambda`, if any, otherwise, it is the value of the variable in the global environment. This policy may coincide with the usual understanding of "dynamic scope".

  After local variables are established, expr_1 through expr_n are evaluated in turn. The special variable `%%`, representing the value of the preceding expression, is recognized. `throw` and `catch` may also appear in the list of expressions.

  `return` cannot appear in a lambda expression unless enclosed by `block`, in which case `return` defines the return value of the block and not of the lambda expression, unless the block happens to be expr_n. Likewise, `go` cannot appear in a lambda expression unless enclosed by `block`.

  `lambda` quotes its arguments; the double-single-quote operator `''` defeats quotation.

  Examples:

  - A lambda expression can be assigned to a variable and evaluated like an ordinary function.

      (%i1) f: lambda ([x], x^2);
                                            2
      (%o1)                    lambda([x], x )
      (%i2) f(a);
                                      2
      (%o2)                          a

  - A lambda expression may appear in contexts in which a function evaluation is expected.

      (%i3) lambda ([x], x^2) (a);
                                      2
      (%o3)                          a
      (%i4) apply (lambda ([x], x^2), [a]);
                                      2
      (%o4)                          a
      (%i5) map (lambda ([x], x^2), [a, b, c, d, e]);
                              2   2   2   2   2
      (%o5)                 [a , b , c , d , e ]

  - Argument variables are local variables. Other variables appear to be global variables. Global variables are evaluated at the time the lambda expression is evaluated, unless some special evaluation is forced by some means, such as `''`.

      (%i6) a: %pi$
      (%i7) b: %e$
      (%i8) g: lambda ([a], a*b);
      (%o8)                   lambda([a], a b)
      (%i9) b: %gamma$
      (%i10) g(1/2);
                                   %gamma
      (%o10)                       ------
                                     2
      (%i11) g2: lambda ([a], a*''b);
      (%o11)                lambda([a], a %gamma)
      (%i12) b: %e$
      (%i13) g2(1/2);
                                   %gamma
      (%o13)                       ------
                                     2

  - Lambda expressions may be nested. Local variables within the outer lambda expression appear to be global to the inner expression unless masked by local variables of the same names.

      (%i14) h: lambda ([a, b], h2: lambda ([a], a*b), h2(1/2));
                                                         1
      (%o14)    lambda([a, b], h2 : lambda([a], a b), h2(-))
                                                         2
      (%i15) h(%pi, %gamma);
                                   %gamma
      (%o15)                       ------
                                     2

  - Since `lambda` quotes its arguments, lambda expression `i` below does not define a "multiply by `a`" function. Such a function can be defined via `buildq`, as in lambda expression `i2` below.

      (%i16) i: lambda ([a], lambda ([x], a*x));
      (%o16)            lambda([a], lambda([x], a x))
      (%i17) i(1/2);
      (%o17)                  lambda([x], a x)
      (%i18) i2: lambda([a], buildq([a: a], lambda([x], a*x)));
      (%o18)    lambda([a], buildq([a : a], lambda([x], a x)))
      (%i19) i2(1/2);
                                           x
      (%o19)                   lambda([x], -)
                                           2
      (%i20) i2(1/2)(%pi);
                                     %pi
      (%o20)                         ---
                                      2

  - A lambda expression may take a variable number of arguments, which are indicated by `[L]` as the sole or final argument. The arguments appear within the function body as a list.

      (%i1) f : lambda ([aa, bb, [cc]], aa * cc + bb);
      (%o1)          lambda([aa, bb, [cc]], aa cc + bb)
      (%i2) f (foo, %i, 17, 29, 256);
      (%o2)       [17 foo + %i, 29 foo + %i, 256 foo + %i]
      (%i3) g : lambda ([[aa]], apply ("+", aa));
      (%o3)             lambda([[aa]], apply(+, aa))
      (%i4) g (17, 29, x, y, z, %e);
      (%o4)                  z + y + x + %e + 46

Function: local (v_1, ..., v_n)

  Declares the variables v_1, ..., v_n to be local with respect to all the properties in the statement in which this function is used.

  `local` quotes its arguments. `local` returns `done`.

  `local` may only be used in `block`, in the body of function definitions or `lambda` expressions, or in the `ev` function, and only one occurrence is permitted in each.

  `local` is independent of `context`.

Option variable: macroexpansion

  Default value: `false`

  `macroexpansion` controls whether the expansion (that is, the return value) of a macro function is substituted for the macro function call. A substitution may speed up subsequent expression evaluations, at the cost of storing the expansion.

  `false`

    The expansion of a macro function is not substituted for the macro function call.

  `expand`

    The first time a macro function call is evaluated, the expansion is stored. The expansion is not recomputed on subsequent calls; any side effects (such as `print` or assignment to global variables) happen only when the macro function call is first evaluated. Expansion in an expression does not affect other expressions which have the same macro function call.

  `displace`

    The first time a macro function call is evaluated, the expansion is substituted for the call, thus modifying the expression from which the macro function was called. The expansion is not recomputed on subsequent calls; any side effects happen only when the macro function call is first evaluated. Expansion in an expression does not affect other expressions which have the same macro function call.

  Examples

  When `macroexpansion` is `false`, a macro function is called every time the calling expression is evaluated, and the calling expression is not modified.

      (%i1) f (x) := h (x) / g (x);
                                        h(x)
      (%o1)                     f(x) := ----
                                        g(x)
      (%i2) g (x) ::= block (print ("x + 99 is equal to", x), return (x + 99));
      (%o2) g(x) ::= block(print("x + 99 is equal to", x),
                                                        return(x + 99))
      (%i3) h (x) ::= block (print ("x - 99 is equal to", x), return (x - 99));
      (%o3) h(x) ::= block(print("x - 99 is equal to", x),
                                                        return(x - 99))
      (%i4) macroexpansion: false;
      (%o4)                         false
      (%i5) f (a * b);
      x - 99 is equal to x
      x + 99 is equal to x
                                  a b - 99
      (%o5)                       --------
                                  a b + 99
      (%i6) dispfun (f);
                                        h(x)
      (%t6)                     f(x) := ----
                                        g(x)

      (%o6)                         done
      (%i7) f (a * b);
      x - 99 is equal to x
      x + 99 is equal to x
                                  a b - 99
      (%o7)                       --------
                                  a b + 99

  When `macroexpansion` is `expand`, a macro function is called once, and the calling expression is not modified.

      (%i1) f (x) := h (x) / g (x);
                                        h(x)
      (%o1)                     f(x) := ----
                                        g(x)
      (%i2) g (x) ::= block (print ("x + 99 is equal to", x), return (x + 99));
      (%o2) g(x) ::= block(print("x + 99 is equal to", x),
                                                        return(x + 99))
      (%i3) h (x) ::= block (print ("x - 99 is equal to", x), return (x - 99));
      (%o3) h(x) ::= block(print("x - 99 is equal to", x),
                                                        return(x - 99))
      (%i4) macroexpansion: expand;
      (%o4)                        expand
      (%i5) f (a * b);
      x - 99 is equal to x
      x + 99 is equal to x
                                  a b - 99
      (%o5)                       --------
                                  a b + 99
      (%i6) dispfun (f);
                                        h(x)
      (%t6)                     f(x) := ----
                                        g(x)

      (%o6)                         done
      (%i7) f (a * b);
                                  a b - 99
      (%o7)                       --------
                                  a b + 99

  When `macroexpansion` is `expand`, a macro function is called once, and the calling expression is modified.

      (%i1) f (x) := h (x) / g (x);
                                        h(x)
      (%o1)                     f(x) := ----
                                        g(x)
      (%i2) g (x) ::= block (print ("x + 99 is equal to", x), return (x + 99));
      (%o2) g(x) ::= block(print("x + 99 is equal to", x),
                                                        return(x + 99))
      (%i3) h (x) ::= block (print ("x - 99 is equal to", x), return (x - 99));
      (%o3) h(x) ::= block(print("x - 99 is equal to", x),
                                                        return(x - 99))
      (%i4) macroexpansion: displace;
      (%o4)                       displace
      (%i5) f (a * b);
      x - 99 is equal to x
      x + 99 is equal to x
                                  a b - 99
      (%o5)                       --------
                                  a b + 99
      (%i6) dispfun (f);
                                       x - 99
      (%t6)                    f(x) := ------
                                       x + 99

      (%o6)                         done
      (%i7) f (a * b);
                                  a b - 99
      (%o7)                       --------
                                  a b + 99

Option variable: mode_checkp

  Default value: `true`

  When `mode_checkp` is `true`, `mode_declare` checks the modes of bound variables.

Option variable: mode_check_errorp

  Default value: `false`

  When `mode_check_errorp` is `true`, `mode_declare` calls error.

Option variable: mode_check_warnp

  Default value: `true`

  When `mode_check_warnp` is `true`, mode errors are described.

Function: mode_declare (y_1, mode_1, ..., y_n, mode_n)

  `mode_declare` is used to declare the modes of variables and functions for subsequent translation or compilation of functions. `mode_declare` is typically placed at the beginning of a function definition, at the beginning of a Maxima script, or executed at the interactive prompt.

  The arguments of `mode_declare` are pairs consisting of a variable and a mode which is one of `boolean`, `fixnum`, `number`, `rational`, or `float`. Each variable may also be a list of variables all of which are declared to have the same mode.

  If a variable is an array, and if every element of the array which is referenced has a value then `array (yi, complete, dim1, dim2, ...)` rather than

      array(yi, dim1, dim2, ...)

  should be used when first declaring the bounds of the array. If all the elements of the array are of mode `fixnum` (`float`), use `fixnum` (`float`) instead of `complete`. Also if every element of the array is of the same mode, say `m`, then

      mode_declare (completearray (yi), m))

  should be used for efficient translation.

  Numeric code using arrays might run faster by declaring the expected size of the array, as in:

      mode_declare (completearray (a [10, 10]), float)

  for a floating point number array which is 10 x 10.

  One may declare the mode of the result of a function by using `function (f_1, f_2, ...)` as an argument; here `f_1`, `f_2`, ... are the names of functions. For example the expression,

      mode_declare ([function (f_1, f_2, ...)], fixnum)

  declares that the values returned by `f_1`, `f_2`, ... are single-word integers.

  `modedeclare` is a synonym for `mode_declare`.

Function: mode_identity (arg_1, arg_2)

  A special form used with `mode_declare` and `macros` to declare, e.g., a list of lists of flonums, or other compound data object. The first argument to `mode_identity` is a primitive value mode name as given to `mode_declare` (i.e., one of `float`, `fixnum`, `number`, `list`, or `any`), and the second argument is an expression which is evaluated and returned as the value of `mode_identity`. However, if the return value is not allowed by the mode declared in the first argument, an error or warning is signalled. The important thing is that the mode of the expression as determined by the Maxima to Lisp translator, will be that given as the first argument, independent of anything that goes on in the second argument. E.g., `x: 3.3; mode_identity (fixnum, x);` yields an error. `mode_identity (flonum, x)` returns 3.3 . This has a number of uses, e.g., if you knew that `first (l)` returned a number then you might write `mode_identity (number, first (l))`. However, a more efficient way to do it would be to define a new primitive,

      firstnumb (x) ::= buildq ([x], mode_identity (number, x));

  and use `firstnumb` every time you take the first of a list of numbers.

Option variable: transcompile

  Default value: `true`

  When `transcompile` is `true`, `translate` and `translate_file` generate declarations to make the translated code more suitable for compilation.

  `compfile` sets `transcompile: true` for the duration.

Function: translate (f_1, ..., f_n)
Function: translate (functions)
Function: translate (all)

  Translates the user-defined functions f_1, ..., f_n from the Maxima language into Lisp and evaluates the Lisp translations. Typically the translated functions run faster than the originals.

  `translate (all)` or `translate (functions)` translates all user-defined functions.

  Functions to be translated should include a call to `mode_declare` at the beginning when possible in order to produce more efficient code. For example:

      f (x_1, x_2, ...) := block ([v_1, v_2, ...],
          mode_declare (v_1, mode_1, v_2, mode_2, ...), ...)

  where the x_1, x_2, ... are the parameters to the function and the v_1, v_2, ... are the local variables.

  The names of translated functions are removed from the `functions` list if `savedef` is `false` (see below) and are added to the `props` lists.

  Functions should not be translated unless they are fully debugged.

  Expressions are assumed simplified; if they are not, correct but non- optimal code gets generated. Thus, the user should not set the `simp` switch to `false` which inhibits simplification of the expressions to be translated.

  The switch `translate`, if `true`, causes automatic translation of a user's function to Lisp.

  Note that translated functions may not run identically to the way they did before translation as certain incompatabilities may exist between the Lisp and Maxima versions. Principally, the `rat` function with more than one argument and the `ratvars` function should not be used if any variables are `mode_declare`'d canonical rational expressions (CRE). Also the `prederror: false` setting will not translate.

  `savedef` - if `true` will cause the Maxima version of a user function to remain when the function is `translate`'d. This permits the definition to be displayed by `dispfun` and allows the function to be edited.

  `transrun` - if `false` will cause the interpreted version of all functions to be run (provided they are still around) rather than the translated version.

  The result returned by `translate` is a list of the names of the functions translated.

Function: translate_file (maxima_filename)
Function: translate_file (maxima_filename, lisp_filename)

  Translates a file of Maxima code into a file of Lisp code. `translate_file` returns a list of three filenames: the name of the Maxima file, the name of the Lisp file, and the name of file containing additional information about the translation. `translate_file` evaluates its arguments.

  `translate_file ("foo.mac"); load("foo.LISP")` is the same as `batch ("foo.mac")` except for certain restrictions, the use of `''` and `%`, for example.

  `translate_file (maxima_filename)` translates a Maxima file maxima_filename into a similarly-named Lisp file. For example, `foo.mac` is translated into `foo.LISP`. The Maxima filename may include a directory name or names, in which case the Lisp output file is written to the same directory from which the Maxima input comes.

  `translate_file (maxima_filename, lisp_filename)` translates a Maxima file maxima_filename into a Lisp file lisp_filename. `translate_file` ignores the filename extension, if any, of `lisp_filename`; the filename extension of the Lisp output file is always `LISP`. The Lisp filename may include a directory name or names, in which case the Lisp output file is written to the specified directory.

  `translate_file` also writes a file of translator warning messages of various degrees of severity. The filename extension of this file is `UNLISP`. This file may contain valuable information, though possibly obscure, for tracking down bugs in translated code. The `UNLISP` file is always written to the same directory from which the Maxima input comes.

  `translate_file` emits Lisp code which causes some declarations and definitions to take effect as soon as the Lisp code is compiled. See `compile_file` for more on this topic.

  See also `tr_array_as_ref`, `tr_bound_function_applyp`, `tr_exponent`, `tr_file_tty_messagesp`, `tr_float_can_branch_complex`, `tr_function_call_default`, `tr_numer`, `tr_optimize_max_loop`, `tr_semicompile`, `tr_state_vars`, `tr_warnings_get`, `tr_warn_bad_function_calls`, `tr_warn_fexpr`, `tr_warn_meval`, `tr_warn_mode`, `tr_warn_undeclared`, `tr_warn_undefined_variable`, and `tr_windy`.

Option variable: transrun

  Default value: `true`

  When `transrun` is `false` will cause the interpreted version of all functions to be run (provided they are still around) rather than the translated version.

Option variable: tr_array_as_ref

  Default value: `true`

  If `translate_fast_arrays` is false, array references in Lisp code emitted by `translate_file` are affected by `tr_array_as_ref`. When `tr_array_as_ref` is `true`, array names are evaluated, otherwise array names appear as literal symbols in translated code.

  `tr_array_as_ref` has no effect if `translate_fast_arrays` is `true`.

Option variable: tr_bound_function_applyp

  Default value: `true`

  When `tr_bound_function_applyp` is `true`, Maxima gives a warning if a bound variable (such as a function argument) is found being used as a function. `tr_bound_function_applyp` does not affect the code generated in such cases.

  For example, an expression such as `g (f, x) := f (x+1)` will trigger the warning message.

Option variable: tr_file_tty_messagesp

  Default value: `false`

  When `tr_file_tty_messagesp` is `true`, messages generated by `translate_file` during translation of a file are displayed on the console and inserted into the UNLISP file. When `false`, messages about translation of the file are only inserted into the UNLISP file.

Option variable: tr_float_can_branch_complex

  Default value: `true`

  Tells the Maxima-to-Lisp translator to assume that the functions `acos`, `asin`, `asec`, and `acsc` can return complex results.

  The ostensible effect of `tr_float_can_branch_complex` is the following. However, it appears that this flag has no effect on the translator output.

  When it is `true` then `acos(x)` is of mode `any` even if `x` is of mode `float` (as set by `mode_declare`). When `false` then `acos(x)` is of mode `float` if and only if `x` is of mode `float`.

Option variable: tr_function_call_default

  Default value: `general`

  `false` means give up and call `meval`, `expr` means assume Lisp fixed arg function. `general`, the default gives code good for `mexprs` and `mlexprs` but not `macros`. `general` assures variable bindings are correct in compiled code. In `general` mode, when translating F(X), if F is a bound variable, then it assumes that `apply (f, [x])` is meant, and translates a such, with apropriate warning. There is no need to turn this off. With the default settings, no warning messages implies full compatibility of translated and compiled code with the Maxima interpreter.

Option variable: tr_numer

  Default value: `false`

  When `tr_numer` is `true` numer properties are used for atoms which have them, e.g. `%pi`.

Option variable: tr_optimize_max_loop

  Default value: 100

  `tr_optimize_max_loop` is the maximum number of times the macro-expansion and optimization pass of the translator will loop in considering a form. This is to catch macro expansion errors, and non-terminating optimization properties.

Option variable: tr_semicompile

  Default value: `false`

  When `tr_semicompile` is `true`, `translate_file` and `compfile` output forms which will be macroexpanded but not compiled into machine code by the Lisp compiler.

System variable: tr_state_vars

  Default value:

      [transcompile, tr_semicompile, tr_warn_undeclared, tr_warn_meval,
      tr_warn_fexpr, tr_warn_mode, tr_warn_undefined_variable,
      tr_function_call_default, tr_array_as_ref,tr_numer]

  The list of the switches that affect the form of the translated output. This information is useful to system people when trying to debug the translator. By comparing the translated product to what should have been produced for a given state, it is possible to track down bugs.

Function: tr_warnings_get ()

  Prints a list of warnings which have been given by the translator during the current translation.

Option variable: tr_warn_bad_function_calls

  Default value: `true`

  - Gives a warning when when function calls are being made which may not be correct due to improper declarations that were made at translate time.

Option variable: tr_warn_fexpr

  Default value: `compfile`

  - Gives a warning if any FEXPRs are encountered. FEXPRs should not normally be output in translated code, all legitimate special program forms are translated.

Option variable: tr_warn_meval

  Default value: `compfile`

  - Gives a warning if the function `meval` gets called. If `meval` is called that indicates problems in the translation.

Option variable: tr_warn_mode

  Default value: `all`

  - Gives a warning when variables are assigned values inappropriate for their mode.

Option variable: tr_warn_undeclared

  Default value: `compile`

  - Determines when to send warnings about undeclared variables to the TTY.

Option variable: tr_warn_undefined_variable

  Default value: `all`

  - Gives a warning when undefined global variables are seen.

Option variable: tr_windy

  Default value: `true`

  - Generate "helpfull" comments and programming hints.

Function: compile_file (filename)
Function: compile_file (filename, compiled_filename)
Function: compile_file (filename, compiled_filename, lisp_filename)

  Translates the Maxima file filename into Lisp, executes the Lisp compiler, and, if the translation and compilation succeed, loads the compiled code into Maxima.

  `compile_file` returns a list of the names of four files: the original Maxima file, the Lisp translation, notes on translation, and the compiled code. If the compilation fails, the fourth item is `false`.

  Some declarations and definitions take effect as soon as the Lisp code is compiled (without loading the compiled code). These include functions defined with the `:=` operator, macros define with the `::=` operator, `alias`, `declare`, `define_variable`, `mode_declare`, and `infix`, `matchfix`, `nofix`, `postfix`, `prefix`, and `compfile`.

  Assignments and function calls are not evaluated until the compiled code is loaded. In particular, within the Maxima file, assignments to the translation flags (`tr_numer`, etc.) have no effect on the translation.

  filename may not contain `:lisp` statements.

  `compile_file` evaluates its arguments.

Function: declare_translated (f_1, f_2, ...)

  When translating a file of Maxima code to Lisp, it is important for the translator to know which functions it sees in the file are to be called as translated or compiled functions, and which ones are just Maxima functions or undefined. Putting this declaration at the top of the file, lets it know that although a symbol does which does not yet have a Lisp function value, will have one at call time. `(MFUNCTION-CALL fn arg1 arg2 ...)` is generated when the translator does not know fn is going to be a Lisp function.

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