Monads/Maybe monad: Difference between revisions
Added Delphi example
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MaiconSoft (talk | contribs) (Added Delphi example) |
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(bind (bind (unit nil) opt_add_3) opt_str) ; evaluates to {:value nil}
</lang>
=={{header|Delphi}}==
{{libheader| System.SysUtils}}
{{Trans|Go}}
<lang Delphi>
program Maybe_monad;
{$APPTYPE CONSOLE}
uses
System.SysUtils;
type
TmList = record
Value: PInteger;
function ToString: string;
function Bind(f: TFunc<PInteger, TmList>): TmList;
end;
function _Unit(aValue: Integer): TmList; overload;
begin
Result.Value := GetMemory(sizeof(Integer));
Result.Value^ := aValue;
end;
function _Unit(aValue: PInteger): TmList; overload;
begin
Result.Value := aValue;
end;
{ TmList }
function TmList.Bind(f: TFunc<PInteger, TmList>): TmList;
begin
Result := f(self.Value);
end;
function TmList.ToString: string;
begin
if Value = nil then
Result := 'none'
else
Result := value^.ToString;
end;
function Decrement(p: PInteger): TmList;
begin
if p = nil then
exit(_Unit(nil));
Result := _Unit(p^ - 1);
end;
function Triple(p: PInteger): TmList;
begin
if p = nil then
exit(_Unit(nil));
Result := _Unit(p^ * 3);
end;
var
m1, m2: TmList;
i, a, b, c: Integer;
p: Tarray<PInteger>;
begin
a := 3;
b := 4;
c := 5;
p := [@a, @b, nil, @c];
for i := 0 to High(p) do
begin
m1 := _Unit(p[i]);
m2 := m1.Bind(Decrement).Bind(Triple);
Writeln(m1.ToString: 4, ' -> ', m2.ToString);
end;
Readln;
end.</lang>
{{out}}
<pre> 3 -> 6
4 -> 9
none -> none
5 -> 12</pre>
=={{header|EchoLisp}}==
Our monadic Maybe elements will be pairs (boolean . value), where value is in Maybe.domain.
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