PDP-1 LISP
Amongst the SIMH Software Kits is L. Peter Deutsch's PDP-1 LISP 1.5 implementation. It's quite limited (particularly in terms of memory) and also reads all numbers in octal, but does at least let you enter and evaluate basic expressions.
On Linux, install SIMH from your distribution's package repositories, e.g., sudo apt-get install simh. Download lispswre.zip (that's from the "Lisp" link on the Kits page above) and unpack it. lisp_doc.txt contains instructions.
You need not compile the assembler and assemble the source; the included lisp.rim is the same output you would have generated anyway.
Start the emulator with the pdp1 command and follow the instructions in §3 of lisp_doc.txt to set up the initial machine state. After the final c (continue) command you will not be presented with a prompt, but you can type Lisp expressions to be evaluated. Remember that newlines are ignored; typing a space (▒ in sample input below) after the final closing paren is what triggers evaulation.
Most errors will halt the machine; when this happens you can continue with the c command:
(puls 7 1)▒ HALT instruction, PC: 000005 (STF6) sim> c (plus 7 1)▒ 10
When you're done, Ctrl-E will exit back to the sim> prompt where you can use the q command to exit. To start again from your saved machine state (created during the setup above), start the simulator with pdp1 and at the sim> prompt use the command get lisp.sav followed by c.
The SIMH Users' Guide contains further details about using SIMH.