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