Archive for March 2011

Seven Languages in Seven Weeks – Prolog – Day 1

Sunday, March 27, 2011

Prolog promptI am tackling a third language from the book today. This is Prolog and we are not complete strangers. I remember using it at uni for some lab practices and I can remember we didn’t get along like a house on fire. I found Prolog strange and at odds with imperative mindset I held back then. Now that I am a bit older, I find the fact that language is a bit different appealing and intriguing and I look forward to see why was it designed in such manner and what benefits it’s approach brings.

Day 1 explains the very basic concepts behind the language. It explains its syntax which is very simple. Main constructs are atoms, variables, facts and rules.

%atoms
me.
brother.
mother.
granddad.

%facts
parent(me, mother).
parent(brother, mother).
parent(mother, granddad).

%rules
grandparent(X, Y) :- parent(X, Z), parent(Z, Y).
sibling(X, Y) :- \+(X = Y), parent(X, Z), parent(Y, Z).
% X, Y and Z are variables

No syntax highlighting is available – I guess that the “hip crowd” does not grok Prolog. Read on »

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Seven Languages in Seven Weeks – Io – Day 3

Sunday, March 6, 2011

It is day 3 with Io and the subjects that we are tackling are DSLs (domain specific languages) with a help from metaprogramming and concurrency in Io.

As you can expect Io lends itself very naturally to defining DSLs due to its proverbial flexibility – after all the ability to change practically everything what it does, allows you to change the nature of Io to your specific problem domain.

In book this is explained through a simple example of defining a DSL in 13 lines of code that allows map definition in JSON like syntax. Homework 2 sets a similar but simpler goal of defining a syntax based on brackets that allows definition of lists. So here it is:

HW2: Create a list syntax that uses brackets

squareBrackets := method(
    call message arguments map(value,
        self doMessage(value)
    )
)

aList := [1, 2, 30, "forty"]
aList println
aList at(3) println

Read on »

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