First-class functions: Difference between revisions

=={{header|BBC BASIC}}==

{{works with|BBC BASIC for Windows}}

Strictly speaking you cannot return a ''function'', but you can return a ''function pointer'' which allows the task to be implemented.

<lang bbcbasic> REM Create some functions and their inverses:

DEF FNsin(a) = SIN(a)

DEF FNasn(a) = ASN(a)

DEF FNcos(a) = COS(a)

DEF FNacs(a) = ACS(a)

DEF FNcube(a) = a^3

DEF FNroot(a) = a^(1/3)

dummy = FNsin(1)

REM Create the collections (here structures are used):

DIM cA{Sin%, Cos%, Cube%}

DIM cB{Asn%, Acs%, Root%}

cA.Sin% = ^FNsin() : cA.Cos% = ^FNcos() : cA.Cube% = ^FNcube()

cB.Asn% = ^FNasn() : cB.Acs% = ^FNacs() : cB.Root% = ^FNroot()

REM Create some function compositions:

AsnSin% = FNcompose(cB.Asn%, cA.Sin%)

AcsCos% = FNcompose(cB.Acs%, cA.Cos%)

RootCube% = FNcompose(cB.Root%, cA.Cube%)

REM Test applying the compositions:

x = 1.234567 : PRINT x, FN(AsnSin%)(x)

x = 2.345678 : PRINT x, FN(AcsCos%)(x)

x = 3.456789 : PRINT x, FN(RootCube%)(x)

END

DEF FNcompose(f%,g%)

LOCAL f$, p%

f$ = "(x)=" + CHR$&A4 + "(&" + STR$~f% + ")(" + \

\ CHR$&A4 + "(&" + STR$~g% + ")(x))"

DIM p% LEN(f$) + 4

$(p%+4) = f$ : !p% = p%+4

= p%</lang>

'''Output:'''

<pre>

1.234567 1.234567

2.345678 2.345678

3.456789 3.456789

</pre>