r4 ™ implements
as described in Michael Cowlishaw's book titled 'The Rexx Language. A Practical Approach to Programming [2nd Ed.]'. 
Kilowatt Software L.L.C.'s extensive and free Classic Rexx programming tutorial 
r4 ™ provides the following >Classic Rexx keyword instructions:  
address arg call do drop end exit if interpret iterate leave nop numeric options 
parse procedure pull push queue return say select signal trace Plus, assignment instructions system command lines 
r4 ™ provides the following Classic Rexx builtin functions:  

The following builtin commands are provided with r4 ™ :  
Makebuf Dropbuf Newstack Delstack 
The following example programs are provided with r4 ™ :  
AnnVal Anova Anova2 Asc2html Ascii BJ Caldisp Caldisp2 ChgAll ChangeStr Combine CompVal CsvDef CsvMaker Csv2xml DatePick Deal Difference Easter Factor Factorial FileDef FileExtensions FinCalc Gcm GetContact Hanoi1 Hanoi2 HtmlMiner Intersection KinematicEquations Lcm LoanCalc Lottery Make Messager MetricArea MetricDistance MetricVolume MetricWeight MetricTemperature ParabolaGraph Permute Picker Powers2 PresVal PrimeFactors Prompter QuadraticFormula Qt Rexxtry Roman Sayit Sieve Sqrt Sumdisk TopoSort Union 
Compute compounded value of an annuity (used with Bizzy.TopHat form) Analyze the variance of multiple columns of statistics Analyze the variance of multiple columns of statistics  DETAILED Converts a marked up Ascii text file to HTML Dislays the Ascii character code table Blackjack  can be executed on Palm OS version of Classic Rexx A calendar preparation program A faster calendar preparation program Replace all occurrences of one string, by another An external procedure that emulates the 'changestr' builtin function Mathematical 'combinations'  i.e. C(52,5) Perform compound interest computation (used with Bizzy.TopHat form) Defines a new commaseparated value (CSV) file Generates commaseparated value (CSV) file form and addition program Converts commaseparated value (CSV) files to XML files Demonstration of program that uses DATEPICK.EXE Deals a hand of cards in Bridge format Computes difference between two sets Calculates Easter Identifies all of the factors that can divide a number Calculates factorial File selection dialog  uses FileDlg accessory Discovers file extensions within a folder (directory) Financial ratio computations (used with TopHat) Computes greatest common divisor of two numbers Get contact information (used with Contact.TopHat form) A 'towers of hanoi' program Animated 'towers of hanoi' program Extracts text from an HTML file that is not within tags  an HTML miner Computes intersection of two sets Kinematic equation solver (Physics) Computes least common multiple of two numbers Perform loan computations (used with Bizzy.TopHat form) Picks 6 lottery numbers Perform directives in a make file script Demonstration of program that uses MSGBOX.EXE Metric area conversions (used with Metric.TopHat form) Metric distance conversions (used with Metric.TopHat form) Metric volume conversions (used with Metric.TopHat form) Metric weight conversions (used with Metric.TopHat form) Metric temperature conversions (used with Metric.TopHat form) Prepares a graph of a parabola, using the Poof!™ GraphIt program Mathematical 'permutations'  i.e. P(52,5) Demonstration of program that uses PICKLIST.EXE Shows 'powers of 2' table Perform present value computation (used with Bizzy.TopHat form) Identifies all of the unique prime factors that can divide a number Demonstration of program that uses PROMPT.EXE Computes roots of a quadratic equation Shows the present time in English An interactive REXX shell Converts a number to roman numerals A tiny full function calculator Prime number algorithm  the 'sieve of Eratosthenes' algorithm Computes square root using Newton's algorithm  an external procedure Summarizes disk space usage Topological sort  dependency analysis Computes union of two sets 
r4 ™ includes the following auxiliary modules:  
DatePick FileDlg MsgBox Prompt PickList R4XFORM™ Revu™ TopHat™ 
a date selection accessory a file selection accessory a message box display accessory a simple value prompt accessory a selection list accessory a program that transforms R4 programs to executable modules a colorful text file viewing accessory a fillintheblank form accessory 
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