Name Recipes/Languages/Pico

Synopsis The classical toy language, including a specialized IDE.

Details Syntax Abstract Load Typecheck Evaluate Assembly Compile UseDef ControlFlow Visualize Uninit IDE

Description Pico is a toy language that has been used as example over the years in many projects and disguishes, Pico has a single purpose in life: being so simple that specifications 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 is 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:

• Syntax: Concrete syntax for Pico.
• Abstract: Abstract syntax for Pico.
• Load: Convert a Pico parse tree into a Pico abstract syntax tree.
• Typecheck: Typechecker a Pico program.
• Evaluate: Evaluate a Pico program.
• Assembly: Assembly language for Pico.
• Compile: Compile a Pico program to assembly language.
• UseDef: Compute use-def information for the variables in a Pico program.
• ControlFlow: Compute the control flow graph for a Pico program.
• Visualize: Visualize Pico Control Flow Graphs.
• Uninit: Find unitialized variables in a Pico program.
• IDE: An Integrated Development Environment for Pico.

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 (yes, simplicity comes at a price!).

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