Pico

rascal-0.40.17

Synopsis

The classical toy language, including a specialized IDE.

Description

Pico is a toy language that has been used as example over the years in many projects and disguises. Pico has a single purpose in life: being so simple that specifications (or implementations) of every possible language aspect are so simple that they fit on a few pages. It can be summarized as follows:

• There are two types: natural numbers and strings.

• Variables have to be declared.

• Statements are assignment, if-then-else and while-do.

• Expressions may contain naturals, strings, variables, addition (+), subtraction (-) and concatenation (||).

• The operators + and - have operands of type natural and their result is natural.

• The operator || has operands of type string and its results are also of type string.

• Tests in if-then-else statement and while-statement should be of type natural.

The following aspects of the Pico language will be discussed:

• Abstract
• Assembly
• Compile
• ControlFlow
• Evaluate
• Load
• Syntax
• Typecheck
• Uninit
• UseDef

Examples

Here is a -- not so simple -- Pico program that computes the factorial function:

begin declare input : natural, 
              output : natural,           
              repnr : natural,
              rep : natural;
      input := 14;
      output := 1;
      while input - 1 do 
          rep := output;
          repnr := input;
          while repnr - 1 do
             output := output + rep;
             repnr := repnr - 1
          od;
          input := input - 1
      od
end

Notes:

• Pico programs do not have input/output statements, so we use variables for that purpose.
• Pico has no multiplication operator so we have to simulate it with repeated addition. Simplicity comes at a price.

Benefits

• Pico is such a small, but functionally complete, language that it is easy to demonstrate how to specify its syntax and semantics.

Pitfalls

• Pico is a small programming language, not really a domain specific language. Some aspects of DSL design and implementation are not demonstrated by Pico.