Preprocessing

MyDef implements some preprocessing directives such as to offer conditional compilations. All MyDef preprocessing directives take the form of "$(keyword...)" and it always takes up the entire line.

Conditional switches

These are straight forward $(if)...$(elif)...$(else) switches.

subcode: A(name)
    $(if:name=Hui)
        $call very_specific_behavior
    $(elif:name=None)
        # do nothing
    $(else)
        $call general_behavior

These conditional switches tests the following condtions:

• $(if:0)

  Always false. The block is switched off. It can be used as effective block comment.

• $(if:1)

  Always true. The block is switched on.

• $(if:number:name)

  True if macro $(name) is defined and starts with digits

• $(if:string:name)

  True if macro $(name) is defined and enclosed in quotes, either "..." or '...'

• $(if:hascode:name)

  True if "subcode: name" is defined

In the followin rules, name can be replaced with name:number (e.g. name:4), which means take the first number characters of the macro $(name).

• $(if:name)

  True if macro $(name) is defined and not empty and not 0, false otherwise

• $(if:name in item1,item2,...,itemN)

  True if macro $(name) is equal to one of the itemlist.

• $(if:name in range)

  range is of the form a-z, where a and z is any alphanumeric character. It is true when the first letter of macro $(name) is in the range.

• $(if:name=string)

  True if macro $(name) is equal to "string"

• $(if:name!=string)

  True if macro $(name) is not equal to "string"

• $(if:name>value)

  True if macro $(name) is greater than value numerically

• $(if:name<value)

  True if macro $(name) is less than value numerically

• $(if:name~string)

  True if macro $(name) starts with "string"

In the following rules, cond refers to any of above conditions (following if:)

• $(if:!cond)

  Negate. True become false, and false become true.

• $(if:cond1 or cond2 or ...)

  Or. True if any of the conditions are true.

• $(if:cond1,cond2,...)

  And. True if all the conditions are true.

The above three operations can be combined. And has the highest precedence, followed by Or and Negate. No parentheses are allowed.

Constant repeats

Since it is a merely macro preprocessing, variable loops does not make sense. But simple constant repeats are quite useful.

$(for:name in a,b,c)
    BLOCK

Here BLOCK represents arbitrary number indented lines. BLOCK is repeated 3 times, each time having macro $(name) set to a, b, and c. This is equiallent to:

subcode: A(name)
    BLOCK

$map A, a, b, c

But in a anonymous, more succinct way.

$(for:name in 1..9)
    BLOCK

In this case, BLOCK repeats 9 times, each time macro $(name) takes value of 1 to 9 respectively. MyDef will comply if you try $(for:name in 1..1000) but make sure that is what you mean.