3 ms·

The usual impression of LOGO is that it's all about the turtle, but as it happens, the language has a fair degree of Lisp-iness to it. Nothing like the Lisp mac

The usual impression of LOGO is that it's all about the turtle, but as it happens, the language has a fair degree of Lisp-iness to it. Nothing like the Lisp macro system iirc, but it did lend itself to functional programming and recursive algorithms quite well.

ianbicking 4y ago
Given the nature of variables and blocks in Logo you can do quite a bit. Like say you want to do a modulo-like operation: IF :SIZE > 100 [MAKE "SIZE :SIZE - 100] You could do: TO MODVAR :VARIABLE :AMOUNT IF THING :VARIABLE > :AMOUNT [MAKE :VARIABLE THING :VARIABLE - :AMOUNT] END MODVAR "SIZE 100 But even things like WHILE can be implemented: TO WHILE :COND :BLOCK IF :COND [EVAL :BLOCK WHILE :COND :BLOCK] END And the blocks are just lists, so you could potentially rewrite them. I was looking at Berkeley Logo to remind myself of the commands, and found that CASE (similar to switch) is implemented as a macro: https://github.com/jrincayc/ucblogo-code/blob/26ae6f01105832ced8fcdf05eaf43321765ff374/logolib/case https://github.com/jrincayc/ucblogo-code/blob/26ae6f01105832... – though it seems like it could be implemented just fine as a regular function. Though :caseignoredp is confusing me a bit... it's technically a dynamically-scoped variable that affects many comparison operations, but that wouldn't work with a macro. I wonder if that's a bug from when it was converted from a normal function to a macro.
- ianbicking 4y ago
  Oops, while should be: TO WHILE :COND :BLOCK IF RUNRESULT :COND [RUN :BLOCK WHILE :COND :BLOCK] END But this does fail when you do some things in the block, like [OUTPUT] (equivalent of return). Also looking closer at UCBLogo macros and they are evaluated at runtime in a way I didn't expect. That is, they are expanded at call time, and can self-reference causing repeated expansions (but the expansions are immediately evaluated so the program size isn't effected). But I think they really could have accomplished the same thing more easily with the Tcl uplevel command.
dtagames 4y ago
Technically, it is a Lisp.
- retrocryptid 4y ago
  When I was a LOGO test subject as a kid in ths early 70s, we used various list & text manipulation features of LOGO to build sentence generators and parsers. It wasn't all about the turtle. Very LISPy stuff. IIRC, the machine we used might have been a modified early lisp machine.
xhevahir 4y ago
I looked at a couple of math books several years ago that used Logo, and was quickly turned off by the fact that it didn't have first-class functions--a pretty big limitation for a lisp. I ended up translating the code to either Python or Racket.

ianbicking 4y ago

Given the nature of variables and blocks in Logo you can do quite a bit. Like say you want to do a modulo-like operation: IF :SIZE > 100 [MAKE "SIZE :SIZE - 100] You could do: TO MODVAR :VARIABLE :AMOUNT IF THING :VARIABLE > :AMOUNT [MAKE :VARIABLE THING :VARIABLE - :AMOUNT] END MODVAR "SIZE 100 But even things like WHILE can be implemented: TO WHILE :COND :BLOCK IF :COND [EVAL :BLOCK WHILE :COND :BLOCK] END And the blocks are just lists, so you could potentially rewrite them. I was looking at Berkeley Logo to remind myself of the commands, and found that CASE (similar to switch) is implemented as a macro: https://github.com/jrincayc/ucblogo-code/blob/26ae6f01105832ced8fcdf05eaf43321765ff374/logolib/case https://github.com/jrincayc/ucblogo-code/blob/26ae6f01105832... – though it seems like it could be implemented just fine as a regular function. Though :caseignoredp is confusing me a bit... it's technically a dynamically-scoped variable that affects many comparison operations, but that wouldn't work with a macro. I wonder if that's a bug from when it was converted from a normal function to a macro.

ianbicking 4y ago
Oops, while should be: TO WHILE :COND :BLOCK IF RUNRESULT :COND [RUN :BLOCK WHILE :COND :BLOCK] END But this does fail when you do some things in the block, like [OUTPUT] (equivalent of return). Also looking closer at UCBLogo macros and they are evaluated at runtime in a way I didn't expect. That is, they are expanded at call time, and can self-reference causing repeated expansions (but the expansions are immediately evaluated so the program size isn't effected). But I think they really could have accomplished the same thing more easily with the Tcl uplevel command.

dtagames 4y ago

Technically, it is a Lisp.

retrocryptid 4y ago
When I was a LOGO test subject as a kid in ths early 70s, we used various list & text manipulation features of LOGO to build sentence generators and parsers. It wasn't all about the turtle. Very LISPy stuff. IIRC, the machine we used might have been a modified early lisp machine.

xhevahir 4y ago

I looked at a couple of math books several years ago that used Logo, and was quickly turned off by the fact that it didn't have first-class functions--a pretty big limitation for a lisp. I ended up translating the code to either Python or Racket.