From 4913379bc7c3cb7b84b8ae62c0415e35df4876f4 Mon Sep 17 00:00:00 2001
From: Alex Karle <alex@alexkarle.com>
Date: Wed, 9 Nov 2022 00:38:43 -0500
Subject: [PATCH] repl: Print expr-stmts and drop need for ';'

In the repl, we can drop the requirements on using ';' for most
statements.

By allowing execute to evaluate and print expr-statemtents we go from
this:

> var x = 1;
> print x = 2;
2

to

> var x = 1;
> x = 2
2
> x
2

Nice!
---
 fisl.scm        |  3 +++
 interpreter.scm | 17 ++++++++++++-----
 parser.scm      |  4 +++-
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/fisl.scm b/fisl.scm
index e9cf8f2..1ba683d 100755
--- a/fisl.scm
+++ b/fisl.scm
@@ -12,6 +12,8 @@
 (include "parser.scm")
 (include "interpreter.scm")
 
+(define in-repl #f)
+
 (define (run code)
   (let ((tokens (scan code)))
     (if tokens
@@ -49,6 +51,7 @@
   (let ((argc (length args)))
     (cond
       ((eq? argc 0)
+       (set! in-repl #t)
        (thread-start! (lambda () (run-prompt) (exit 0)))
        (nrepl 1234))
       ((eq? argc 1) (run-file (car args)))
diff --git a/interpreter.scm b/interpreter.scm
index 5f35961..d75af85 100644
--- a/interpreter.scm
+++ b/interpreter.scm
@@ -94,15 +94,18 @@
         (else (runtime-err! (format "Unknown bin op ~A" op))))))
    (else (runtime-err! (format "Unknown expr type ~A" expr)))))
 
+(define (lox-print val)
+  (print (cond
+           ((null? val) "nil")
+           ((eq? val #f) "false")
+           ((eq? val #t) "true")
+           (else val))))
+
 (define (execute stmt)
   (cond
    ((print-stmt? stmt)
     (let ((res (evaluate (print-stmt-value stmt))))
-      (print (cond
-               ((null? res) "nil")
-               ((eq? res #f) "false")
-               ((eq? res #t) "true")
-               (else res)))
+      (lox-print res)
       '()))
    ((var-stmt? stmt)
     (let ((value
@@ -111,6 +114,10 @@
               (evaluate (var-stmt-init stmt)))))
       (hash-table-set! global-env (token-lexeme (var-stmt-name stmt)) value))
     '())
+   ((expr-stmt? stmt)
+    (let ((res (evaluate (expr-stmt-value stmt))))
+      (if in-repl (lox-print res))
+      '()))
    (else (runtime-err! (format "Unknown stmt ~A" stmt)))))
 
 (define (interpret stmts)
diff --git a/parser.scm b/parser.scm
index a37b5c8..41205a6 100644
--- a/parser.scm
+++ b/parser.scm
@@ -87,7 +87,9 @@
   (let-values (((expr toks) (parse-expression '() tokens)))
     (if (top-type? toks '(SEMICOLON))
       (values (maker expr) (cdr toks))
-      (parse-err! (car toks) "expected ;"))))
+      (if in-repl
+        (values (maker expr) toks)
+        (parse-err! (car toks) "expected ;")))))
 
 (define (parse-print-statement tokens)
   (parse-generic-stmt tokens make-print-stmt))
--
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