Eidos: A Simple Scripting Language Benjamin C. Haller Dept. of Computational Biology Cornell University, Ithaca, NY 14853 [email protected] Last revised 27 February 2021, for Eidos version 2.6 (SLiM version 3.6). Acknowledgements: Thanks to the designers of the C, R, and Objective-C languages, which paved the way for Eidos in so many ways. Thanks to Terence Parr for his excellent book Language Implementation Patterns, which guided much of the implementation of Eidos’s tokenizer and parser; and thanks to him also for his grammar of the C language, which provided guidance in the development of Eidos’s grammar. Thanks to Jean Bovet and Terence Parr for ANTLRWorks, which was very helpful in designing Eidos’s grammar, and which generated the railroad diagrams used in this manual. Thanks to Philipp Messer for believing me when I said that adding a whole language to SLiM would make it much cooler. Citation: Haller, B.C. (2016). Eidos: A Simple Scripting Language. URL: http://benhaller.com/slim/Eidos_Manual.pdf URL: http://messerlab.org/slim License: Copyright © 2016–2021 Philipp Messer. All rights reserved. Eidos is a free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. Disclaimer: The program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License (http://www.gnu.org/licenses/) for more details. 2 Contents 1. Eidos overview ................................................................................................................................ 6 1.1 Introduction ............................................................................................................................. 6 1.2 Why Eidos? .............................................................................................................................. 7 1.3 A quick summary of the Eidos language ................................................................................... 8 2. Language features ............................................................................................................................ 9 2.1 Types, literals, and constants .................................................................................................... 9 2.1.1 The integer type ............................................................................................................ 9 2.1.2 The float type ............................................................................................................... 9 2.1.3 The logical type ............................................................................................................ 10 2.1.4 The string type .............................................................................................................. 10 2.2 Vectors .................................................................................................................................... 11 2.2.1 Everything is a vector ................................................................................................... 11 2.2.2 Sequences: operator : ................................................................................................... 11 2.2.3 Concatenation: function c() and type promotion ........................................................... 12 2.2.4 Subsets: operator [] ....................................................................................................... 13 2.3 Expressions .............................................................................................................................. 14 2.3.1 Arithmetic expressions: operator +, -, *, /, %, ^ ............................................................ 14 2.3.2 Logical expressions: operator |, &, ! ............................................................................. 15 2.3.3 Comparative expressions: operator ==, !=, <, <=, >, >= ............................................... 16 2.3.4 String concatenation: operator + .................................................................................. 16 2.3.5 The ternary conditional: operator ?else ......................................................................... 17 2.3.6 Nested expressions: precedence and the use of () for grouping ..................................... 18 2.4 Variables ................................................................................................................................. 19 2.4.1 Assignment: operator = ................................................................................................ 19 2.4.2 Everything is a vector (a reminder) ................................................................................ 20 2.5 Conditionals ............................................................................................................................ 20 2.5.1 The if statement and testing for equality ........................................................................ 20 2.5.2 The if–else statement .................................................................................................... 22 2.5.3 A digression: the semicolon, ; ....................................................................................... 22 2.5.4 Compound statements with { } ...................................................................................... 22 2.6 Loops ...................................................................................................................................... 23 2.6.1 The while statement ..................................................................................................... 23 2.6.2 The do–while statement ................................................................................................ 24 2.6.3 The for statement .......................................................................................................... 24 2.6.4 The next statement ....................................................................................................... 24 2.6.5 The break statement ..................................................................................................... 25 2.6.6 The return statement ..................................................................................................... 26 2.7 Functions ................................................................................................................................. 27 2.7.1 Calling functions: operator () ........................................................................................ 27 2.7.2 The NULL type ............................................................................................................. 28 2.7.3 The void type ............................................................................................................... 30 2.7.4 The functionSignature() function, and introducing function signatures .......................... 31 2.7.5 Optional arguments and default values ........................................................................ 33 2.7.6 Function signatures summarized .................................................................................. 33 2.7.7 Named arguments in function calls .............................................................................. 34 2.8 Objects .................................................................................................................................... 35 2.8.1 The object type ............................................................................................................. 35 2.8.2 Element access: operator [] and sharing semantics ....................................................... 36 2.8.3 Properties: operator . .................................................................................................... 37 3 2.8.4 Multiplexed assignment through properties: operator = revisited .................................. 38 2.8.5 Comparison with object: operator ==, !=, <, <=, >, >= revisited .................................. 39 2.8.6 Methods: operator . and the methodSignature() method ............................................... 40 2.9 Matrices and arrays .................................................................................................................. 43 2.9.1 Defining matrices and arrays ........................................................................................ 43 2.9.2 Matrix and array attributes ............................................................................................ 45 2.9.3 Using Eidos operators and built-in functions with matrices and arrays .......................... 45 2.9.4 Subsets of matrices and arrays using operator [] ............................................................ 48 2.10 Comments ............................................................................................................................... 51 2.10.1 Single-line comments with // ........................................................................................ 51 2.10.2 Block comments with /* */ ............................................................................................ 51 3. Built-in functions ............................................................................................................................. 52 3.1