ETA
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ETA is an esoteric programming language designed by Mike Taylor in 1999. The name comes from its instruction set, based on the eight most common letters in the English language: E, T, A, O, I, N, S, H. "Eta" is also the seventh letter in the Greek alphabet, and ETA uses base-7 numbering. The language is stack-based and all characters that are not instructions are treated as comments. Eta has 7 instructions:
| Command | What it does |
|---|---|
| E | Pop two numbers of the stack, first b, then a.Then push floor(b/a) first and b%a second. |
| T | Pop 2 numbers off the stack, first addr, then cond. If cond!=0 then jump to the addrth instruction. The first instruction is instruction 1. Jumping to instruction 0 terminates the program.
|
| A | Push the current instruction number. |
| O | Print and pop top of stack as an ASCII character |
| I | Push the input as an ASCII character |
| N | Push a base-7 number. The digits are: H=0 T=1 A=2 O=3 I=4 N=5 S=6. E terminates the number. Example: NTONE=(1x7^2+3x7^1+5x7^0) |
| S | Pop 2 numbers off the stack: first b, then a. Push b-a on the stack. |
| H | Pops a number n from the stack. If n>0 then remove the nth value and push it on top of stack.If n<=0 then push the nth item onto top of stack and keep the original one intact unlike the top case. If n=0, this is effectively a DUP. |