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March 31, 2026 15:08
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lisp interpreter
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| #!/usr/bin/env bash | |
| # terrible lisp interpreter | |
| # | |
| # example run: | |
| # | |
| # (first (list 1 (+ 2 3) 9))) | |
| # | |
| # evaluating + 2 3 = 5 | |
| # evaluating list 1 5 9 = 1,5,9 | |
| # evaluating first 1 5 9 = 1 | |
| DEBUG=true | |
| output_path=/tmp/parsed | |
| usage() { | |
| cat << USAGE | |
| usage: $0 [path_to_program] | |
| example program: | |
| (first (list 1 (+ 2 3) 9)) | |
| example output: | |
| 1 | |
| USAGE | |
| exit 1 | |
| } | |
| source="$1" | |
| [[ -f "$source" ]] || usage | |
| rm -rf "$output_path" | |
| mkdir -p "$output_path" | |
| tokenizer() { | |
| local acc char | |
| emit() { | |
| [[ -n "$acc" ]] && echo "$acc" | |
| acc= | |
| } | |
| # loop character by character | |
| while IFS= read -rn 1 char; do | |
| char=${char:- } # newlines become spaces | |
| case $char in | |
| '(' | ')') | |
| emit | |
| echo "$char" | |
| ;; | |
| ' ') emit ;; | |
| # accumulate characters | |
| *) acc="${acc}${char}" ;; | |
| esac | |
| done | |
| } | |
| lexer() { | |
| local i=0 | |
| cd "$1" | |
| while read -r token; do | |
| case "$token" in | |
| '(') | |
| read -r token | |
| mkdir "$i.$token" | |
| pushd "$i.$token" &> /dev/null | |
| ;; | |
| ')') popd &> /dev/null ;; | |
| *) touch "$i.$token" ;; | |
| esac | |
| ((i++)) | |
| done | |
| } | |
| show_ast() { | |
| cd "$1" | |
| tree . -v --noreport \ | |
| | sed 's/[0-9]\+ //' | |
| } | |
| cat "$source" \ | |
| | tokenizer \ | |
| | lexer "$output_path" | |
| # show_ast "$output_path" | |
| evaluate() { | |
| local fn=${1#*.} | |
| pushd "$1" &> /dev/null | |
| local file | |
| local -a args | |
| # DFS to resolve our args | |
| while read -r file; do | |
| if [[ -d "$file" ]]; then | |
| local returned=${ evaluate "$file"; } | |
| local arg | |
| while read -r arg; do | |
| args+=("${arg#*.}") | |
| done <<< "$returned" | |
| else | |
| args+=("${file#*.}") | |
| fi | |
| done < <(ls | sort -n) | |
| $DEBUG && echo -n "evaluating $fn ${args[@]} = " 1>&2 | |
| execute() { | |
| case "$fn" in | |
| '') # root function | |
| printf '%s\n' "${args[@]}" | |
| ;; | |
| '+') # sum all arguments | |
| local acc=0 | |
| for arg in "${args[@]}"; do | |
| ((acc+=arg)) | |
| done | |
| echo $acc | |
| ;; | |
| list) # pass through? | |
| printf '%s\n' "${args[@]}" | |
| ;; | |
| first) | |
| echo "${args[0]}" | |
| ;; | |
| esac | |
| } | |
| local result=${ execute; } | |
| echo "$result" | |
| $DEBUG && echo "$result" | paste -sd, 1>&2 | |
| popd &> /dev/null | |
| } | |
| run() { | |
| $DEBUG && { | |
| echo "running '$source'" | |
| cat "$source" | |
| echo | |
| } 1>&2 | |
| cd "$1" | |
| evaluate * | |
| } | |
| run "$output_path" |
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because of lines 96 and 129, this requries bash 5.3+
if you change the
${ }to$( )it will work on older versions (not sure how old tho lol)