From 82e1570c2cf4c8ffac25101db330e38adac94635 Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Sun, 11 Jan 2026 16:37:01 -0500
Subject: [PATCH 1/2] feat: add file input flag to CLI.

Added -f flag to allow reading lambda expressions from files.

Changes:
- Add FileSource type to read from file paths.
- Add -f flag to command-line parser.
- Implement validation to prevent conflicting -f and positional arguments.
---
 internal/config/parse_from_args.go | 27 +++++++++++++++++----------
 internal/config/source.go          | 12 ++++++++++++
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/internal/config/parse_from_args.go b/internal/config/parse_from_args.go
index 6a2b688..41f738e 100644
--- a/internal/config/parse_from_args.go
+++ b/internal/config/parse_from_args.go
@@ -12,21 +12,28 @@ func FromArgs() (*Config, error) {
 	explanation := flag.Bool("x", false, "Explanation. Whether or not to show all reduction steps.")
 	statistics := flag.Bool("s", false, "Statistics. If set, the process will print various statistics about the run.")
 	profile := flag.String("p", "", "CPU profiling. If an output file is defined, the program will profile its execution and dump its results into it.")
+	file := flag.String("f", "", "File. If set, read source from the specified file.")
 	flag.Parse()
 
-	// There must only be one input argument.
-	if flag.NArg() == 0 {
-		return nil, fmt.Errorf("no input given")
-	} else if flag.NArg() > 1 {
-		return nil, fmt.Errorf("more than 1 command-line argument")
-	}
-
 	// Parse source type.
 	var source Source
-	if flag.Arg(0) == "-" {
-		source = StdinSource{}
+	if *file != "" {
+		// File flag takes precedence.
+		if flag.NArg() > 0 {
+			return nil, fmt.Errorf("cannot specify both -f flag and positional argument")
+		}
+		source = FileSource{Path: *file}
+	} else if flag.NArg() == 0 {
+		return nil, fmt.Errorf("no input given")
+	} else if flag.NArg() > 1 {
+		return nil, fmt.Errorf("more than 1 command-line argument")
 	} else {
-		source = StringSource{Data: flag.Arg(0)}
+		// Positional argument.
+		if flag.Arg(0) == "-" {
+			source = StdinSource{}
+		} else {
+			source = StringSource{Data: flag.Arg(0)}
+		}
 	}
 
 	return &Config{
diff --git a/internal/config/source.go b/internal/config/source.go
index 9996f0c..758eaa0 100644
--- a/internal/config/source.go
+++ b/internal/config/source.go
@@ -27,3 +27,15 @@ func (s StdinSource) Extract() (string, error) {
 
 	return string(data), nil
 }
+
+// A source reading from a file.
+type FileSource struct{ Path string }
+
+func (s FileSource) Extract() (string, error) {
+	data, err := os.ReadFile(s.Path)
+	if err != nil {
+		return "", err
+	}
+
+	return string(data), nil
+}
-- 
2.49.1


From 9ab004bec4b3a0f56692c15db0350c3dd5198bdb Mon Sep 17 00:00:00 2001
From: "M.V. Hutz" <git@maximhutz.me>
Date: Sun, 11 Jan 2026 16:40:39 -0500
Subject: [PATCH 2/2] refactor: use -f flag in Makefile targets.

---
 Makefile | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 45742d2..7f15f78 100644
--- a/Makefile
+++ b/Makefile
@@ -20,13 +20,13 @@ build:
 	chmod +x ${BINARY_NAME}
 
 run: build
-	./${BINARY_NAME} - < ./samples/$(TEST).txt > program.out
+	./${BINARY_NAME} -f ./samples/$(TEST).txt > program.out
 
 profile: build
-	./${BINARY_NAME} -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
+	./${BINARY_NAME} -p profile/cpu.prof -f ./samples/$(TEST).txt > program.out
 
 explain: build
-	./${BINARY_NAME} -x -p profile/cpu.prof - < ./samples/$(TEST).txt > program.out
+	./${BINARY_NAME} -x -p profile/cpu.prof -f ./samples/$(TEST).txt > program.out
 
 graph:
 	go tool pprof -raw -output=profile/cpu.raw profile/cpu.prof
-- 
2.49.1