qsp_parser/documentation/typing.md

QSP Type system

Internally, there is only two types in the engine : String and Integer. This is represented with this C struct :

typedef struct
{
    union
    {
        QSPString Str;
        int Num;
    } Val;
    QSP_TINYINT Type;
} QSPVariant;

Variables and assignation

The type of a variable is determined by the first character in the name:

#define QSP_STRCHAR QSP_FMT("$")

// …

#define QSP_VARBASETYPE(name) (*(name).Str == QSP_STRCHAR[0]) /* QSP_TYPE_STRING | QSP_TYPE_NUMBER */

But during the assignation, a conversion is automatically done when the types does not match :

INLINE void qspSetVar(QSPString name, QSPVariant *val, QSP_CHAR op)
{
    …
    if (QSP_VARBASETYPE(name) != QSP_BASETYPE(val->Type))
    {
        if (!qspConvertVariantTo(val, QSP_VARBASETYPE(name)))
        {
            qspSetError(QSP_ERR_TYPEMISMATCH);
            return;
        }
        qspSetVarValueByReference(var, index, val);
    
    }

This can raise uncontrolled error with some functions like INPUT if you directly the result into a numeric variable.

Conversion and comparaison between values

Most of the functions provide automatic conversion between them: a string will be converted in integer if the other operand is an integer:

• math operation

  That’s why '1' + 1 will give the result 2 and not '11'

• comparaison

  For example, the source code for the comparaison is the following one:

  case qspOpEq:
      QSP_NUM(tos) = QSP_TOBOOL(qspAutoConvertCompare(args, args + 1) == 0);
      break;
  

When string cannot be converted into a number, the number will be converted in string, and the comparaison will compare thoses two strings. In the ASCII table, a text will always be greater than a number ('a' > 9999 will return -1 and '$' > 0 will return 0)

Explicit conversion

From string to integer

isnum(…) will tell you if a value is an integer or not:

isnum('123') -> -1
isnum('abc') -> 0

Using val(…) you can convert a string into a integer:

val('123') -> 123
val('abc') -> 0     ! No error here

From integer to string

str(…) will convert a number in string.

QSP Syntax Parser

[!NOTE]
This parts describe how QSP Syntax Parser deal with the type system. This is not a part of the language reference.

No implicit conversion

Explicit is better than implicit.

Implicit conversion is a bad thing. It can raise errors during the game if you don’t care, and can hide other error in the code:

This code is valid, but does not work as expected (because of a $ is missing in the if clause, $myvar and myvar are two differents variables):

$myvar = 'VALUE'
…
if myvar = 'VALUE':
    …

In order to spot this kind of errors, a warning will be raised here.

The boolean type

I’ve added a boolean type which does not exists in the original syntax. In QSP, the value -1 stand for True and 0 for False.

Because Readability counts. , the application will raise a warning if a String or an integer is directly given in an if clause. A comparaison operator is required.