I started in on Build your own list and ran into the same problem.
None of the above answers worked for me. After a little research I found out that macOs doesn't have the gnu readline library that provides the readline functions, Different versions of MacOs provide emulation of readline using a library called editline. to begin...
man editline
#include <histedit.h>
Ok, editline gives you some structs for line input and history,
and functions to operate on them. First you have to instantiate these structs. The documentation for editline is not very helpful because it doesn't contain any examples. Apple makes the header file available so that helps a little. http://www.opensource.apple.com/source/libedit/libedit-13/src/histedit.h
I am new to this and it was still pretty confusing to me. there is some version of the source code to libedit available as a debian package. Fortunately someone wiser than I has already dug into it and implemented a command line using lbedit. His code is here: https://www.cs.utah.edu/~bigler/code/libedit.html.
I took Mr Bigler's code, and the code from Build your own list, and put them together to get this.
/* repl-macos.c
* Repl code example from builyourownlisp.com
* Modified by NB aug 2017
* Code example for editline from
* www.cs.utah.edu/~bigler/code/libedit.html
*/
#include <stdio.h>
#include <string.h>
#include <histedit.h>
char* prompt(EditLine *e){
return "lispy> ";
}
int main(int argc, char** argv){
EditLine *el; // Line editor state
History *herstory; // the rest is history
// Temp Variables
int count;
const char *usrin;
int keepreading = 1;
HistEvent ev;
// Initialize the editline state
el = el_init(argv[0], stdin, stdout, stderr);
el_set(el, EL_PROMPT, &prompt);
el_set(el, EL_EDITOR, "emacs");
// Initialize history
herstory = history_init();
if(!herstory){
fprintf(stderr, "Couldn't initialize history\n");
return 1;
}
//set history size
history(herstory, &ev, H_SETSIZE, 800);
// Set up the call back functions for history functionality
el_set(el, EL_HIST, history, herstory);
puts("Begin moLisp interpreter");
puts("Type 'exit' at prompt to exit");
while(keepreading){
usrin = el_gets(el, &count);
// add the command to the history, and echo it back to the user
if(count > 0){
history(herstory, &ev, H_ENTER, usrin);
if(strcmp(usrin, "exit\n"))
printf("No, You're a %s", usrin);
else{
puts("bye");
--keepreading;
}
}
}
// Clean up memory
// by freeing the memory pointed to within the structs that
// libedit has created.
history_end(herstory);
el_end(el);
return 0;
}
Notice: The instantiation of the structs that are used happens outside of
the while loop, and so do the functions that free the memory those structs are using. Because of this, I added the command to exit, otherwise I think there's a memory leak if the only way to exit the while loop is by interrupting the program. To compile:
gcc repl-macos.c -ledit -Wall -o repl-edit
-ledit is needed to link editline
If it has any relevance, I am using macOs 10.4.11
and here's my compiler, output of
gcc --version
powerpc-apple-darwin8-gcc-4.0.0 (GCC) 4.0.0 20041026 (Apple Computer, Inc. build 4061)
Now the only problem with this, and the book points this out, is that
c-code is supposed to be portable and this isn't. The next step would be to add preprocessor directives so that it uses readline on linux and editline on macos.
