At the end of the line

PM adopts a clean approach to statement separation. PM statements are formally separated by semicolons. However, these may be omitted if the next statement starts on a new line. This is the only syntactic role for line breaks – statements and expressions may sprawl across as many lines as you wish. For die-hard C/C++/Java programmers, it is also possible to add a semicolon at the end of a statement list.

 a=1; b=2; c=1  
 x = -b + sqrt( b**2 - 4 * a * c) /  
                  2*a  
 print("x="//x)

Semicolons are also used in constructors for two-dimensional data structures: arrays and matrices. Line breaks can be substituted for semicolons here too, enabling you to write something like:

 id_matrix = ( 1,0,0  
               0,1,0  
               0,0,1 )

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Compile time, run time, coffee time

[ Please note that in the following discussion I will be using PM 0.5 notation, which is slightly different to PM 0.4 and also in some flux as PM 0.5 is still in development. ] Many programming languages (and most newly developed ones) include some form of compile-time programming, ranging from simple preprocessors ( #define , #if in C) to fully blown macro systems capable of re-writing the abstract syntax tree during compilation (Rust, Julia, etc .). In line with its philosophy of keeping things as simple as possible, but not simpler, PM takes a middle road with compile-time programming supported primarily through the type system. There is nothing too radical here – this is not an area where the language aims to break new ground. The PM approach centres around the use of compile-time types. Many languages use special types to denote literal values and PM follows this trend. Literal integers, reals, strings and Booleans each have their own types: literal(int) , litera...

The PM Type System

In common with other aspects of PM design, the type system is designed to facilitate the use of flexible programming constructs, such as polymorphism and dynamic dispatch, while emphasising the generation of fast, static, code. In common with many other modern languages, PM also attempts to combine the safety of static typing with the expressivity of dynamically typed languages such as Python . The type of any PM expression may usually be determined by a static examination of the code. Variables take their types from an initialising expression using the ‘:=’ declaration syntax popularised by Go . a:= 100 ! Declare ‘a’ as an integer (int) variable Variables do not change type during the course of their lifetime – polymorphic programming requires the use of special values, described later. Composite values such as structures are generated using specialised expressions rather than through the invocation of type-specific creator functions: b:= struct var_descriptor...

All change .. not quite

With the recent release of PM 0.4 and the positive reception to my PM presentation at CIUK2023 , it seems like a good time to bring back the PM blog after a long hiatus. Another good reason for its resurrection is that I feel that I now have built the basic semantics of the language into something like a coherent whole, giving me something concrete to write about. There have been a few major changes to the language since my last blog entry. The main syntactic change has been the shift from keyword-delimited control statements to curly-brackets. This is not a statement on my part as to the merits of the two approaches, I am generally agnostic in this debate which can border on the religious. It was simply that with the way that the language was developing, the keyword approach was getting cumbersome – frequently used constructs were taking up far to much space and impeding readability. PM now uses curly brackets to terminate statements and semicolons to separate (and optionally terminat...

PM Programming Language

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