Copyright (C) 2017, 2018, H. Conrad Cunningham

Acknowledgements: I originally created these slides in Fall 2017 to accompany what is now Chapter 43, Calculator: Modular Structure, in the 2018 version of the textbook Exploring Languages with Interpreters and Functional Programming.

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Lecture Goals

• Examine the modular structure of Calculator language interpreter

Calculator Language Modules

Values Module

• Values module Values (Ch. 42)

  Secret: specific representation for values supported by language

Environments Module

• Environments module Environments (Ch. 42)

  Secret: specific representation for environments used by interpreter

Abstract Syntax Module

• Abstract_Synax module AbSynCalc (Ch. 42)

  Centralize definitions of abstract syntax

Evaluator Module

• Evaluator module EvalCalc (Ch. 42)

  Secret: implementation of language semantics

Lexical Analyzer Module

• Lexical_analyzer module LexCalc common to both parsers (Ch. 44)

  Secret: lexical structure of concrete language (identifiers, literal constants, operators, etc.)

Parser Modules

• Parser abstract module (Ch. 44)

  Secret: how concrete syntax recognized and translated to abstract syntax

  • Prefix syntax Parser module ParsePrefixCalc

  • Infix syntax Parser module ParseInfixCalc

REPL Modules (1)

Haskell IO program

1. Read an input from the command line.

   If the input is an exit command, exit; else continue.

2. Evaluate the expression after parsing.

3. Print the resulting value.

4. Loop back to step 1.

REPL Modules (2)

• Uses Parser and Evaluator modules

• Separate versions

  • infix: InfixCalcREPL

  • prefix: PrefixCalcREPL

• Expressons plus REPL commands :set, :display, :quit

Key Ideas

• Modular structure for Calculator language interpreter

  • 7 modules

  • cohesive units

  • secrets

  • abstract interfaces