4tH, the friendly Forth compiler J.L. Bezemer July 14, 2021 Contents 1 What’s new 19 I Getting Started 24 2 Overview 25 2.1 Introduction . 25 2.2 History . 25 2.3 Applications . 26 2.4 Architecture . 26 2.4.1 The 4tH language . 28 2.4.2 H-code . 28 2.4.3 H-code compiler . 29 2.4.4 Error handling . 30 2.4.5 Interfacing with C . 30 3 Installation Guide 32 3.1 About this package . 32 3.1.1 Example code . 32 3.1.2 Main program . 32 3.1.3 Unix package . 33 3.1.4 Linux package . 34 3.1.5 Android package . 38 3.1.6 MS-DOS package . 40 3.1.7 MS-Windows package . 41 3.2 Setting up your working directory . 43 3.3 Now what? . 43 3.4 Pedigree . 43 3.5 Contributors . 44 1 CONTENTS 2 3.6 Questions . 44 3.6.1 4tH website . 44 3.6.2 4tH Google group . 45 3.6.3 Newsgroup . 45 4 A guided tour 46 4.1 4tH interactive . 46 4.2 Starting up 4tH . 46 4.3 Running a program . 47 4.4 Starting an editing session . 47 4.5 Writing your first 4tH program . 48 4.6 A more complex program . 52 4.7 Advanced features . 56 4.8 Suspending a program . 63 4.9 Calculator mode . 65 4.10 Epilogue . 65 5 Frequently asked questions 66 II Primer 69 6 Introduction 70 7 4tH fundamentals 71 7.1 Making calculations without parentheses . 71 7.2 Manipulating the stack . 72 7.3 Deep stack manipulators . 73 7.4 Passing arguments to functions . 73 7.5 Making your own words . 74 7.6 Adding comment . 75 7.7 Text-format of 4tH source . 75 7.8 Displaying string literals . 75 7.9 Creating variables . 76 7.10 Using variables . 76 7.11 Built-in variables . 76 7.12 What is a cell? . 77 7.13 What is a literal expression? . 77 7.14 Declaring arrays of numbers . 77 CONTENTS 3 7.15 Using arrays of numbers . 78 7.16 Copying arrays of numbers . 78 7.17 Declaring and using constants . 78 7.18 Built-in constants . 79 7.19 Using booleans . 80 7.20 IF-ELSE constructs . 80 7.21 FOR-NEXT constructs . 80 7.22 WHILE-DO constructs . 81 7.23 REPEAT-UNTIL constructs . 82 7.24 Infinite loops . 82 7.25 Including source files . 82 7.26 Getting a number from the keyboard . 83 8 4tH arrays 84 8.1 Aligning numbers . 84 8.2 Creating arrays of constants . 84 8.3 Using arrays of constants . 84 8.4 Using values . 85 8.5 Creating string variables . 86 8.6 What is an address? . 86 8.7 String literals . 87 8.8 String constants . 87 8.9 Initializing string variables . 88 8.10 Initializing a NULL string variable . 88 8.11 Getting the length of a string variable . 88 8.12 Printing a string variable . 89 8.13 Copying a string variable . 89 8.14 The string terminator . 89 8.15 Slicing strings . 90 8.16 Appending strings . 91 8.17 Comparing strings . 91 8.18 Finding a substring . 92 8.19 Replacing substrings . 93 8.20 Deleting substrings . 93 8.21 Removing trailing spaces . 94 8.22 Removing leading spaces . 94 8.23 Upper and lower case . 95 CONTENTS 4 8.24 String literals and string variables . 95 8.25 Printing individual characters . 96 8.26 Distinguishing characters . 96 8.27 Getting ASCII values . 97 8.28 Printing spaces . 97 8.29 Fetching individual characters . 98 8.30 Storing individual characters . 98 8.31 Getting a string from the keyboard . 100 9 Character Segment 101 9.1 The Character Segment . 101 9.2 What is the TIB? . 101 9.3 What is the PAD? . 102 9.4 How do I use TIB and PAD? . 102 9.5 Simple parsing . 102 9.6 Converting a string to a number . 104 9.7 Controlling the radix . 104 9.8 Pictured numeric output . 107 9.9 printf() like formatting . 110 9.10 Converting a number to a string . 111 9.11 Aborting a program . 112 9.12 Opening a file . 113 9.13 Reading and writing from/to a file . 114 9.14 Closing a file . ..