CSCE 314 Lecture 11

« previous | Wednesday, September 21, 2011 | next »

Lecture given by T.A. — too much too fast!

Modules

--MyModules/MyModuleName.hs
modulue MyModules.MyModuleName
(exportedFunctions
,otherFunction
,etc
) where

-- definitions

Importing Modules from Files

import MyModules.MyModuleName (optional,list,of,definitions)
-- module aliasing
import MyObscenelyLongModuleName as Name

Example

module Stack (StkType, push, pop, empty) where

data StkType a = EmptyStk | Stk [a]

push x (Stk s) = Stk (x:s)
pop (Stk (_:s) = Stk s
top (Stk (x:_)) = x

-- ...

Programming Language

What is a programming language?

language

language = syntax + semantics

syntax

Form of a program (how expressions, commands, etc are put together to make a final program

defines the set of valid programs

usually specified with a grammar

parser (how sentences are formed from words)

semantics

meaning of a program (how programs behave when executed on a computer)

defines how valid programs behave

informal: documentation and tutorials

formal operational: execution on an abstract machine

formal denotational: meaning as a mathematcal function

Implementation

1. lexer: forms tokens from input stream
2. parser: forms linear array of tokens into abstract syntax tree (AST) or sentence
3. type checker: makes sure AST nodes are used correctly
4. …